


Riptide Lover

by jinglebell



Category: Sherlock (TV)
Genre: BAMF!John, BAMF!Sherlock, Dark Romance, Foot Fetish, Human!John, Interspecies Sex, John herps the wild derp a bit in this tale but redemption happens so bear with him, Johnlock - Freeform, M/M, Male multiple orgasms, Merlock, Mermaid Sex, Mythical Beings & Creatures, Oral Sex, Possessive Sherlock, Sherlock AU, Sherlock is a big slut but only for John, Stockholm Syndrome, abstract mentions of rape, animal death (food), aqua peen hunger force, dubious consent and morality, handjobs, historical fantasy & paranormal romance, let's make creative use of merman anatomy, merfolk are not dainty sea sirens and are actually quite dangerous, mermaid au, merman!Sherlock, mermen are big sluts, mermen really get the best of both worlds, mild gore warning, moments of dubious and awkward interspecies consent, rough sex and rough waters ahead with a very happy ending, size queen, steampunk mad science, switch!lock, victorian au
Language: English
Status: In-Progress
Published: 2014-09-18
Updated: 2016-03-31
Packaged: 2018-02-17 14:32:33
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings, Graphic Depictions Of Violence
Chapters: 19
Words: 113,393
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/2312978
Author URL: https://archiveofourown.org/users/jinglebell/pseuds/jinglebell
Summary: <blockquote class="userstuff">
              <p>
  <i>The year is 1866. When John becomes swept overboard, he never expects to encounter a living creature of myth. When the merman absconds with John, the lost sailor must use every tool at his disposal to convince Sherlock not to kill him. But it seems that killing John Watson is not what the deadly, beautiful creature has in mind at all...</i>
</p><p> </p><p>Victorian mermaid AU. Heed the tags. <b>Check <a href="http://jinglebellfic.tumblr.com/tagged/riptide-lover">blog</a> for update schedule; I update a bit sporadically due to work and how much time writing this monster takes! Be forewarned, might want to hold off reading until I finish it if you aren't a patient reader!</b></p>
            </blockquote>





	1. The Misfortune of John Watson

**Author's Note:**

  * For [Anarfea](https://archiveofourown.org/users/Anarfea/gifts).



> Greetings, or as a dolphin might say: _clickity-click squeak squeak_! I hope you enjoy my latest multi-chaptered story, in which John and Sherlock are put in an even more peculiar world than that one time I wrote [alien mindsex](http://archiveofourown.org/works/2157390). I have no idea what brought this on. Story's dark, so be a responsible reader and check the tags before indulging!

[ ](http://jinglebellfic.tumblr.com/tagged/riptide-lover)

John Watson was drowning. ****

Ocean water roiled up around him, churning in violent smashing waves that buffeted the sailor's body about like a cat playing with an errant fluff. He was desperate to keep his face aloft, sucking in salty gasps of air when he could and closing his mouth and eyes when the next inevitable wave folded over him.

After a long day of fighting the storm on board the ship, John's muscles felt like pudding. It was like swimming through molasses -- every sluggish movement seemed to contribute only to the inevitable sink, and he was taking in more salt water than air at this point. In the distance, a ribbon of lightning rippled across the sky and cast the ship's silhouette in brief relief against the storm-darkened sky.  _HMS Endymion_ was an enormous English woodscrew frigate - but so far out on the ocean that she looked like a child's toy.

John had been on the water for nineteen of his thirty-two years. Like all sailors, John well knew that his love for the ocean did not protect him from its wrath. The water was a fickle mistress. And the sea had swallowed John Watson straight off the deck of the ship he was contracted to, and sucked him away on the rain-rattled waves until all hope was lost. 

Still, it was not in John's character to give up without a struggle.

So he paddled.

A large wave bloomed. John inhaled deeply and closed his mouth as it crested, high enough to blacken the sky, and crashed down -- hammering John underwater like a nail into wood. The moment he was shoved into the deep, he became aware of the absence of sound. Everything was muffled, here. The water rushing in John's ears was almost  preferable to the rattling of the rain, the boom of thunder, and the slosh of water rutting into the sky. His body spun, and then, rather disastrously, was caught up by a strong current and hurtled sideways. Bubbles streamed from his mouth and John's peripheral vision was lost to haze and sparks.

The storm raged on the surface, a distance far greater than John could ever hope to swim. He sank into the deep.The water pressure was different this deep. Heavier. _Well old boy,_ thought John to himself, _you've had a good run_. For a sailor, dying in the ocean was not an unexpected way to go. Despite this macabre thought, John could not bring himself to give up entirely, and he kicked with his remaining strength. 

It was right around then that a flash of lightning illuminated a shape in the deep.

The shape circled John, looping a predatory ellipse around him as John looked on in stupefaction, certain that it was a shark. Couldn't the thing bloody wait until he was actually dead to feast upon his flesh? It was true that no corpse lasted long in the ocean, but the indignity of being turned into fish food before he had even properly _croaked_ bothered John -- bothered him more than his own impending expiration. He tried to turn, to keep the fish in his vision, but sparks danced behind his eyes with the effort. He went still to conserve his oxygen.

A second flash of lightning lit up the deep.

What John saw in the water not six feet from him boggled the mind. The fish circling him was no shark, but a creature, an amalgamation whose likeness appeared only in myth. John's exhausted mind sifted through sedimentary piles of memory for the appropriate descriptor, and finally offered up... 'mermaid'.

If he’d had the air to spare, John might have laughed in astonishment.

Suddenly, the mermaid whipped its tail and was scant inches from him. This close, John could see even without the sporadic luminescence of the storm above, and what he observed made John amend his initial assumption that this creature was a maid. The creature had the countenance of a man, albeit an uncommon looking one. It was pale as a pearl, with a Patrician nose and cheekbones sharp as glass. Its lips were generous and soft, with a distinct v-shaped bow of Cupid in the upper.

A spattering of dark scales streaked up the creature's forehead to blend seamlessly into his hairline. And he had hair! Just as a human did, floating in a dark corona around his face. His eyes were the silver-green color of fish scales. He stared at John, lower lids squinting up with the intensity of his regard.

John stared back in incredulity.

He noticed gills flexing open and closed under the hinge of the merman’s jawline.

 _What a pretty creature._  The burning in John's lungs had faded and was replaced by numbness. His fingers and toes were accosted by tiny needles, and his eyelids grew heavy without oxygen.His body convulsed without permission, freeing a cascade of bubbles from his mouth which flowed off of the merman's face where he floated above John.

Frightfully strong hands tightened around John's biceps and marble-cool lips sealed over his. A slick tongue dipped into the seam of his mouth and coaxed John's numb lips open to the sting of salt, establishing an airtight seal. The merman breathed into him, pushing a gush of briny, stale air into John's starved lungs. John inhaled greedily through the channel of their connected mouths, unable to be picky about the method of delivery, and returned to consciousness with a desperate jolt.

The merman drew back and regarded John. Hungry for a second breath to ease the burn in his lungs, John paddled after the implausible creature. The merman lashed his tail and glided just out of John’s reach, and the cruel smirk that manifested on his face informed John that he was being mocked. The carrot of life-bringing air was being dangled right in front of him. He was playing with John, a cat playing with a half-dead shrew. 

That.

That was just _not on,_ and it made John furious. One didn't revive a man on the brink of death just to watch them die anew. His lungs stuttered, a screaming alert. His heart beat frantic against the cage of his ribs, but John knew he had only one chance for survival -- so he settled his body into a deliberate and misleading stillness, even though it was against his every instinct. 

The merman cocked his head to the side and when he drifted in close John struck. He snatched the capricious creature's wrist in his rough grip. The merman had the obvious advantage of him in the water, but John had been a sailor for almost two decades: his arms were ropey and strong, corded with muscle from hauling, from hoisting, from reeling and pounding. The merman's eyes were wide with shock and he twisted violently, but John tightened his hand until he felt the merman's wrist bones bones slide together.

He needed that air. If the creature would not give it to him, by god John would take it.

He gripped the merman's jaw with bruising force, thumb sliding clumsily into the delicate folds of his gills, and fit their mouths together so hard that teeth clinked. Something sharp sliced John's lower lip and he was too desperate for breath to stop and assess the injury. The merman refused to open to him, mouth twisted in displeasure, but John bit his lower lip and pulled until he opened.  _Come on. I know you have what I need, you damned fish._

There was a heartbeat's pause. The merman had gone very still in the cold water, and John became aware of his tail windmilling beneath them. This close, the merman's silver eyes blurred in John’s vision; their hair tangled together in the current, blond against black.

At last the merman breathed for him.

John made a low noise of pure relief, even though it cost him a bubble. The merman tolerated John's desperate spluttering as he exhaled bubbles into the sea and then jammed his mouth against those cold lips to refill. In this way, John sucked up enough stale air to clear his head.

After some time, the merman jerked his head minutely; an unspoken indication that he would prefer to be released. John's body was quivering with adrenaline and new oxygen. The high he experienced made it difficult to think clearly, but John realized that the merman was his only hope for survival. There was no way he was getting to the surface on his own. Just as this occurred to John, the merman tapped him and pointed surfaceward. John loosened his grip, and before he could second-guess his choice the merman dragged him up, up, up with great haste. The merman gripped underneath John's armpits and shoved him the last few feet out into the ozone-spiced air.

John flailed free of the ocean with a graceless splash. His first few breaths were mostly water, and he coughed terribly, and then vomited seawater, but he couldn't be arsed to care. Anything, anything, in order to breathe once more. It felt so good. When the excess water was out of his system, John tipped onto his back and floated in euphoria.

The storm had passed and John saw the black clouds roiling away in the distance. The ocean had calmed and the waves seemed gentle and, to John's perception, almost apologetic. Gone were the thunder and lightning, and the celestial carpet of the night sky glittered above him.  _I am an insignificant speck, and I am alive. I am alive._

The merman's head emerged from the water. He was observing John closely, but John barely noticed. He had experienced his fair share of near-drowning experiences, but after this one, the novelty of breathing took on new pleasure.

_I am alive!_

John delighted in the feeling of sensation pouring back into his body. He reveled in the painful, convulsive shivers of thermoregulation. He bobbed in the water, and let out a primal shout, a great whoop of undiluted joy. Then he began to laugh, and one he started he simply could not stop. He turned to look at the merman, the only person nearby with whom John might share this moment of unadulterated gratitude.

The merman was staring at John as though he had gone round the twist. John took one look at that quizzical alien face and laughed all the harder. It was too much. Too much stimulation and the danger of it all, the brush with death and scrabbling, clawing his way back from the brink –- cor, meeting a bloody _merman!_ It made him feel exquisitely alive, so he rolled in the water and hooked his hand around the back of the merman's head. Dark hair had cascaded into sleek black curls, revealing the fans of webbed fins where a man would have ears. Chuckling breathlessly, John reeled him in close and disregarded the warning hiss. He kissed the merman full on the lips firmly once, twice, thrice and then released him with an exaggerated smacking sound. The merman jerked away roughly. His transparent inner eyelids blinked.

“I'm alive!” John told the merman. He didn't recognize his own voice.

The merman had brought his fingers to his lips, touching them as though he wasn't entirely sure what had just happened. John grinned stupidly. 

“I'm _alive,_ ” he repeated.

“ _..._ Yes,” the merman agreed slowly, as though John were an especially dim-witted child. He had an unexpectedly deep vocal timbre.  _He can speak!_ John thought elatedly.

John laughed again, but then his body seized up and he abruptly sank under the surface and drew in a fresh lungful of water. The merman caught him and pulled him aloft. John spluttered and coughed and retched out all the water, gripping the slick skin of the merman's shoulders for support.

Water still trickling from his mouth, John stared into the creature's pallid face. “Help me. Take me somewhere dry.”

The merman considered his request, sloe-eyed and calculating. This close, John could see that the pupils of his eyes were horizontal, enough to bring to mind a cuttlefish. John was giddy. Despite being stranded in the middle of the ocean after a terrible storm, kept only from death's clutches by a sadistic creature straight out of legend, John felt himself invincible. What more could this merman possibly do to him? He had lost his ship, and nearly lost his life. The threat the merman posed was an electric hint of danger along the fine hairs of his arms.

The merman said, “The fish would have you.”

“Pardon?” said John.

“If I let go of you, you will sink like the debris from your ship. The fish will feast upon your flesh... countless small bites, until nothing is left but your bones. I could keep them for my collection.”

The merman stared guilelessly up at him, still supporting John's weight above water as though it was nothing. His face looked so innocent in that moment, utterly incongruous with his perilous remark. But there was mischief in the fiend's expression, and a gleam of self-awareness that encouraged John to call bluff.

“Don't play with me,” reprimanded John. It was an absurd thing to tell a merman out in the middle of the bloody ocean, in hindsight. “You -- you know better, you wouldn't do that.”

John was not actually certain that the merman did know better, and that he wouldn't drown John on a whim. The merman leaned back and gazed at John from beneath a lace of thick black lashes. “Wouldn't I? It would be easy to kill you.”

“Yes,” agreed John mildly. “It would. But I would really appreciate it if you'd help me get to land. You're quite strong, I know you can do it.”

The merman's grip under his arms tightened at that.  _Cor_ , but the creature was strong! John could feel the ripple and flex of swimmer's muscles. A thrill of interest tingled up his spine and he quashed it down, blaming it on his newfound appreciation for life. The merman still seemed to be thinking.

“Will you take me?” asked John again. His adrenaline-fueled elation was fading. “Please?”

The merman's gills flared. “I will take you to dry land... but on one condition.”

“Anything,” replied John, and instantly wished he could bite the words back into his mouth.

Those plush lips stretched into a wide, eerie smile that exposed pointed teeth. “I have questions about your kind. If I take you to dry land, you will answer all of them. You will promise this now.”

“Blazes! Yes, yes. Take me to dry land.”

“You will _promise_ this now,” repeated the merman, urgently.

“I promise to answer all your questions!” cried John. “Now, take me --!”

The rest of John's demand was cut off as the merman rolled in the water, tugging John's arms about his neck. Then John felt the pulse of the merman's tail and they were off like a silver arrow, slicing effortlessly through the waves with speed. John clung like a barnacle, holding his breath against the salt spray on his face. He thought he must look absurd, but like any man John appreciated a fast ride.

Still, the novelty of travel in this manner faded after nearly fifteen unbroken minutes.

He estimated that they were traveling at twenty-six knots, and that was astounding. His arms ached where they clutched the creature's strong shoulders, and not for the first time John thanked the stars he was a sailor, hewn from ocean rock, and no simpering gentry on a pleasure cruise. 

More time passed. Perhaps another twenty minutes, John could not be sure, as his focus was concentrated fully on holding on tight.

The chill of shock and exertion weighed on him. But the water _was_ getting warmer, gradually, and clearer. By the watery pink light of dawn, John could see land on the horizon and he whooped weakly with joy. The merman slowed his pace, his body obscured by the dark water below John.

It was an island.

A medium-sized one, possessing of vegetation and a beach with sugar-white sand. But it was not to the shoal that the merman delivered John. He swam past the seductive sand. John struggled to unlace his numb fingers, but he was too weak to swim the distance.  _Wait, you are passing by the dry land!_  Desperation stole his words. He wanted to be set free onto that virgin sand, to feel it between his toes. Instead, the merman brought to the opposite side of the island.

They entered a lagoon, a place where shallow water was separated from the sea by narrow gravel shoals connected to the island.

The temperature difference between the open ocean and the shallow water made John groan, unbidden. It was _warm_. The merman's tail was kicking up great clouds of sand, for he was almost too large to swim properly in water this shallow. John's aching fingers finally deigned to cooperate, and he floated free, reaching with his feet for the bottom. His toes just barely touched the silt.

The merman had positioned himself bodily between John and the open sea. The shoals led to an unscalable cliff face. Wet black rocks glistened with algae, limpets, and brine. The still water extended into a cave that gaped open like a whale mouth, a marine ballroom studded with bring stalactites.

 _A grotto. Well. There had better be dry land in here_ , John thought tiredly, glowering at the merman as he took buoyant steps along the ocean floor. He felt the merman follow him in, and the sun rose behind them over the ocean, heralding the dawn of a new day.


	2. Sherlock

**Notes for the Chapter:**

> Gasp! Posting the update a day early, just because I want to! <3 Enjoy, and please check out the updated tags. Now that I have written more of the story, I have a better idea of where it's going and was able to tag in advance before you get hooked. (Get it? _Hooked_? Like, a fish hook, because - uh, yeah, all right I'll let you read.)

John looked around in astonishment, for the grotto was incredible.

The water was clearer than crystal, like a pane of expensive glass. The rock formation possessed a natural skylight, through which John could see morning gulls spiralling in the sky. A flat rock the length of a hansom protruded in the center of the cave like a central island. Many similar rocks created a ziggurat of primitive steps that formed the back wall of this chamber, steps which led up and into the shrug of darkness. Several of these stone steps were steeper than John was tall.  _This place is large enough to hold a small opera_ , he mused. _A marine opera house -- imagine that! The aristocrats of London would go mad for the novelty_.

The sea was shallower, here, perhaps three or four feet deep. So long had John been weightless in the water that the gravity of air nearly undid him, and he staggered under his own weight trying to get onto the flat rock. He managed to get about halfway onto it when he gave up and lay there gratefully with his cheek pressed to the stone, bare feet still dangling.

Every muscle in his body ached, and every bone around which they wrapped ached, and within his bones John was certain that his marrow ached too. It was with great effort that John turned his head to look for his rescuer. A dark shape floated in the shade near the grotto’s mouth. As John watched, a fin sluiced briefly above the surface.

John had so many questions, but he did not even have the energy to remove his white linen trousers, or his shredded shirt (held on by the grace of his braces alone). Lulled by the sound of rippling water, he fell asleep.

~  ~

Heat woke him.

It felt like someone had rubbed salt over the inside of his throat, and his stomach squeezed tight to his spine with hunger. His cheek was numb where it squashed against the rock, and a hot beam of sunlight burnt his back from the hole in the cave roof. John ignored the shrieking protest of his muscles and lifted himself into a push-up with a groan. He flipped onto his back and stared up into the sun. It was a blinding pinprick of whiteness in improbable blue.

He stared until white circles danced behind his eyes.

“You're awake.”

The deep baritone startled John and he surged to a seated position. He regretted the swift movement for it made his head slosh like a stormy sea. The merman floated beside the rock, silver-green eyes affixed keenly on John.

“You are dehydrated,” the merman added a moment later. His gaze flicked from John's face to the rock, and John reluctantly followed the gesture to see a conch shell had been set beside him, along with an amberjack splayed open from gill to fin and spread like an offering. Rather than being repulsed by the thought of raw fish, John's stomach grumbled in anticipation.

“Drink. Eat," commanded the merman. John didn't need to be told twice. He took up the heavy conch and peered inside.

“It's rainwater,” explained the merman impatiently. “Safe for your own kind to drink.”

John pitched it back. He drank, and drank until every last crevice of the conch was dry. The merman drew closer. Fueled by his hunger, John dipped into the amberjack, curling his fingers into the marbled fat and stripping it off the tiny bones. He could not get the meat to his mouth quickly enough, and was delighted to discover that the fish was so fresh it seemed to melt on his tongue -- rich as butter, oily and spicy with blood.

John could not honestly say whether it was the obligation of his hunger or the quality of the catch that made it so good. Perhaps it was his mythological dining companion, who observed John’s meal with scientific detachment. John ate until his belly was full and the fish was a pile of crumpled skin and spine, and then he licked his fingers clean. With hydration and satiation came a clarity of mind that had been heretofore absent.

“Sweet Mary, you're enormous,” remarked John, nearly interrupting himself with an inaudible belch. He sat back and looked at the creature.

The merman snorted air across the sea surface. His tail undulated gently behind him, parallel to the ocean floor. In the light of day, John could see the entire length of the creature's body. Although he had the torso of a human man, the merman's fish tail was much longer and heavier than any illustration John had ever seen. It was hard to tell from this angle, but John estimated that tail was nearly three meters long.

“And you are so tiny,” the merman told him. “To kill you would be easy.”

Entertaining a post-prandial bliss, John was hardly as discomfited by that comment as he ought to have been. “That may be so,” he said affably. “But if you kill me, you'll never get to ask me questions about my people. And don't think I don't see what you're up to."

The merman betrayed his intrigue with raised brow. “And what is that?”

“You're trying to keep me from leaving. Otherwise, you would have put me on the beach. Like I asked.”

This remark was met with a warning tone of voice from the creature, who replied: “You asked me to take you to dry land. I have done so.”

John got the sinking feeling that he had unwittingly got himself into greater trouble than he had foreseen. “You know what I meant. This isn't fair.”

The merman's gills fanned open on either side of his neck.

John was reminded of the time that some of his fellow sailors had acquired small, brightly colored freshwater fishes from Siam. They were aggressive animals that would quarrel if put in a bowl with another of their kind. The sailors used to bet on them. It had never held any especial interest for John, but seeing the merman's flaring jostled the memory free like a loosened tooth.

“Fair?” hissed the merman. “Choose carefully your next words, human. You made a promise to me in exchange for your own life. If you do not uphold your own end of the bargain, _I will eat you_.”

Cor! John recalled with perilous clarity the predator teeth hidden behind the creature’s lips, and fear pulled hard behind his navel. They regarded each other tensely.

“All right,” murmured John at last. “All right, calm down. No reason to get into collie shangles about it. I did promise you. I just... it's been quite a lot. I've lost my ship, and I've lost my bearings. I have no idea where I am, or how I am still alive, or –- begging your pardon, what you _are_. Up until now, I had no idea there was anything in the entire world like you.”

The merman's demeanor softened. 

“It is so. You are beholden to me,” he crooned as though he was agreeing with something John had said. His gills flattened back into a somewhat normal neck again. “You may answer some questions now.”

“I, ah. All right. If you don't mind, I've got some questions for you as well."

John stretched his arms over his head to show the merman he was getting comfortable, and winced at the salty crackle of his shirt where it had baked dry. His braces dug into his shoulders and he shrugged out of them, letting them fall to bracket his hips. The merman rolled slowly onto his back in the water. This exposed the narrow length of his torso to John's perusal. He had two sets of gills: there were the small ones that flexed under his jawline, and then there were deep slits along his ribs. They were as pink as a woman's sex and slick like that, too. It was clear even to John, who had no experience with biology, that these latter gills were the engine powering this creature's anatomy.

“Ask,” said the merman.

“Well, what is your name?” inquired John. The surprised look he got made John chuckle. “What did you think I was going to ask?” 

The merman ignored John’s second question. “It is known that I am called Sherlock.”

“ _Sherlock_!” echoed John. “That's an unusual name. Well, not for a … for your people, I suppose.”

“It's unusual amongst even mine own people,” granted Sherlock. “What is... your own name?”

“John Watson.”

“Johnwatson.”

“No, it's –- ah, hmm. We have two names, in my culture. A first name –- for me, that's 'John', and a surname, which belongs to our family. 'Watson'. But please, just call me John.”

“John,” agreed Sherlock.

“Thank you. Were you going to let me die out there?”

Sherlock's response was insultingly flippant. “Possibly.”

“Then why on earth did you give me air?” demanded John in a rush of righteous indignation.

“To test a hypothesis. I have seen many humans drown. I wanted to see if mine own self-converted air would be sufficient to sustain human life.”

John blinked. “Oh.” That made sense, in a twisted and scientific sort of way. “I see –- no! No, no, _no_. You've seen other humans drown before?”

“Yes,” Sherlock's eyes glittered dangerously.

John decided to drop that line of questioning. He tried a different topic. “Howcan you produce air?"

This query was met with a long pause that John strongly suspected had to do with Sherlock trying to think in English. “Hm. In addition to gills, mine own people have lungs similar to your own kind. I hyper-respirated to convert air from inside mine own body, and oxygen from the water, into air. Notice: you did not die. I would be interested in testing how long a human could sustain life from that alone,” said Sherlock craftily.

“I would not be interested in testing that,” John parried coolly. “Do you use your lungs often?”

“To assist in buoyancy and as a stabilizing agent, primarily. Are you male?”

John blinked twice again. “What?”

“What is your own sex? Are you male?”

John couldn't help it. He laughed. “Yes! What, can't you tell?”

Sherlock squinted at him. “Males and females of your own kind look the same, and wear extraneous coverings besides. I -- I just wanted to be certain.”

John giggled and the noise seemed to delight Sherlock, who sat up in the water with the two little fins framing his face perked up.

“What are those? Ears?” John wanted to know, gesturing automatically at his own ears. 

Sherlock canted his head to the side. “They serve that function, although their main function is... superfluous.”

“How is it superfluous?” asked John. He scooted closer to the edge of the rock, dropped his calves over so that his feet landed in the water with a splash. The sun poured in through the skylight as it trundled across the afternoon sky.

“Feels good in the Riptide,” Sherlock said dismissively, waving his hand to indicate that that was not a topic he wished to discuss further. “What is the meaning of that noise you make?”

“Which one?” asked John. Sherlock giggled and it sounded exactly like him, an imitation so perfect that it brought to mind a parrot's mimicry. John flinched.

“Tarnation! That's uncanny. It's a laugh. Uh. Humans laugh when --”

“-- I _know_ about laughs,” Sherlock interjected defensively. “I just wanted to be sure. I hadn't heard a laugh like that before. Do it again.”

John found himself smiling. Sherlock did not smile back, although it seemed to John that his eyes glittered in a more receptive manner than before. 

“I can't laugh on demand.”

Sherlock snorted. “Fine. Your own kind can't breathe underwater. Nor can whales. How long can you hold your own breath?”

“I'm not sure,” John answered honestly. Then, capitalizing on something he had noticed about the merman, he asked, “Would you like to test that?”

When Sherlock's eyes lit up, John knew he had happened upon a potential bargaining chip. “Yes.”

“All right, perhaps we shall. Later, though. Let's get you through your questions first.”

“Promise me.”

Once again, John felt a warning bell go off in his head; every time Sherlock extracted a promise from John, it felt more significant than when a human asked for a commitment. But John dipped his chin in assent. “I promise we can test how long I can hold my breath –- later.”

Sherlock relaxed and looked smug.

John found another question rising unbidden to his lips. “How on earth do you speak the Queen's own English? I mean, that trick you can do –- imitating my voice, it's amazing. I guess I shouldn't be surprised that you picked it up.”

“... _amazing_ ,” echoed Sherlock, lifting his voice out of his own natural baritone and moulding that single word into John’s tenor. It was unnerving to hear his own voice come out of the merman’s mouth. It might have been John's imagination, but it seemed like Sherlock drifted closer. “You think so?”

“Of course it is. Quite incredible, really. How did you learn it?”

“I observed sailors, like you, at port. Mostly.”

“How do you know I'm a sailor?” 

Sherlock rolled his eyes. “Obvious. I did not see you fall off the human ship, but the extraneous things you cover your body with match the sailors I saw at port. Your kind wears different coverings depending upon their rank.”

John silently ceded the point that, though England may not have had a clearly articulated caste system, there was a social hierarchy. 

“You wear clothing like a sailor, and your body is strong. I have not seen a human yet with a body as strong as yours... all the others died straightaway. They didn't like the water,” Sherlock said darkly, eyes narrowed as he gleefully awaited John's reaction. John's stomach turned.

“That's horrible."

Sherlock made an unintelligible noise. He flipped in the water so that only his black curls floated on the surface, peering up through his hair at John. John watched his gills open and close at the hinges of his jaw and wondered how many people he had watched drown. Then Sherlock glided closer, until his face was inches from John's submerged feet. It was with great difficulty that John resisted the urge to yank them away when Sherlock surfaced enough to speak.

“What are these called?”

A giant, webbed hand emerged to cradle John's foot. They both leaned over Sherlock's hand to look at each other; the merman examining the human's foot, and the human staring at the merman's hand. Sherlock's hand was huge, and long, and unexpectedly delicate looking. Transparent silver skin stretched between each finger, which was tipped with a wickedly hooked white claw.

John's foot was, well, a foot. Standard issue equipment really. Small for a man, and callused from gripping the salty deck. “My foot. 'Feet', plural. It's how we move around. Useful for landlubbers.”

John got an idea. He gently pulled his foot out of Sherlock's hand and slid into the water beside the merman, whose presence was so enormous that John felt something like David when he confronted Goliath. John waded to the ziggurat-like steps of the flat rocks that led deep into the cave. The third rock up was almost thirty feet along.

“Do you want to see the human gaits?”

“I do,” admitted Sherlock.

John clambered up onto the first step. Water rushed down his legs from his soaked trousers, causing the fabric to cling. He stood up and turned to look at Sherlock, and... the merman was staring at his legs. The expression on his face was something akin to rapture. If Sherlock were a human man, John would have pegged the expression as lustful.

More confident on land, John grinned down at him and turned back to assess the second step. He put his hands on the edge and used his upper body strength to haul himself quickly up and over, then he rolled to his feet and sprang onto the third step. He narrowly missed a deep crack in the rock. Sherlock hissed, but John was nimble as a monkey, and accustomed to climbing far more difficult terrain.

He stood up and spun around to look down at Sherlock many feet below, with his hands on his hips. John knew he was a good climber. Sherlock regarded him, lips parted in the barest hint of a smile.

John turned and strutted down the rock to the far end, where a curtain of algae had grown down the sheer rock face. Then he turned around and jogged back across the rock. When he reached the other side, he spun rapidly and sprinted back across again. At the last minute, John turned and bounded out into the open air with a great whooping shout. He curled into a ball and landed in the water with a tremendous splash. It was faster than climbing back down, and to be honest John wasn't sure if his arms could manage it twice after the ordeal he'd been through on the frigate.

This last part seemed to delight Sherlock. He swarmed up into John's space before the waves had a chance to calm and snaked his giant body in a circle around John. When he spoke, Sherlock's voice had dropped an entire octave. “Very illuminating.”

John's good humor failed to evaporate. He windmilled his hands to catch his balance. “Thought you might be curious about that. You've probably only seen us walking or swimming before.”

“Correct. May I examine your legs?”

“If I can look at your tail," bartered John, thinking quickly of ways to get the merman to give him back some personal space.

Sherlock smiled sharkily down at him. "Acceptable.”

“You first,” coaxed John, unable to keep the curiosity out of his voice. “I haven't got a good look at you yet, you've been underwater this whole time, or it's been dark.”

Speaking of darkness: the sun was beginning its descent. The light from the skylight had changed from white to gold. The merman swam around John and placed both of his webbed hands on the first rock step. Sherlock rippled his lean body up and onto the rock. The muscles in his forearms corded handsomely with the effort, and John became suddenly aware that although Sherlock was not human, he was bewitching.

Sherlock shuffled forward with his palms flat beneath him. Once his hips were settled, he locomoted briskly, like a seal. It would be a mistake to underestimate his speed on land, John realized with a little thrill.

“Blazes. You’re so big,” breathed John in awe.

The illustrations of merfolk always depicted them with tails that barely were longer than human legs, terminating in two petal-shaped caudal fins like a child's drawing of a fish. Reality was much longer than that. John's initial estimation of three meters' worth in the tail was fairly close. The rock did not have enough room to accommodate Sherlock, and the merman's abdominal muscles flexed prettily when he lifted up his caudal fluke –- the fins that terminated at the end of his tail –- out of the water. Seawater cascaded down, and John could not hold in his gasp.

Sherlock was like nothing John had ever seen before.

And, oh, how John stared.

The slender column of the merman's hips continued down, down, down, into that long and powerful tail. It was ink black, the color of an oil spill –- a black so polished and deep that it reflected the ambient light of the grotto. Liquid purples, and hints of cyan blue gleamed dangerously along the seam of each scale. John came closer that he might get a better look.

The largest scales were rimmed at the tip: a strip of metallic copper that actually glittered like fool's gold. Blazes. Those scales were so reflective that John could see his own reflection, albeit distorted in the inky rainbow.

Sherlock’s tail was possessing of an abundance of plumed fins. Genetics had given the merman a striking gift in his coloration. His fins, in stark contrast to his black tail, were all white. In fact, the scales at the very end of Sherlock's tail transitioned into appaloosa spots, like snowfall, before turning white completely at the fins themselves. 

A single mismatched white scale glimmered on the midportion of Sherlock's tail, and John realized with a mental jolt that he found this aesthetically erotic.  _Like a beauty mark,_ he thought.

There were two pelvic fins fanning out from the inner vee of Sherlock's hips. These fins, to John's eye, looked strong: like the flippers of a seal, although rather more graceful in appearance. These twin fins hugged up against Sherlock's body, dormant. It did not occur to John to wonder whether they had any purpose aside from locomotion.

Sherlock was practically glowing under John’s rapt attention. He had twirled the end of his tail so that the semi-transparent white skin of his caudal fins spread out in a slow arc, and from behind this glimmering fan he gazed coyly at John.

“My god,” murmured John, and his Brutus of a body betrayed him with a twitch of interest. He was grateful for the obfuscation the water provided.

Sherlock smiled. Indulgent, he rotated onto his belly and turned his back to John to show off his dorsal fin. This fin ran over the curve of what would have been Sherlock's arse, were he human. Three strong spines were strung together by a netting of gossamer skin. Sherlock demonstrated his control over this particular fin by flexing the spines open briefly.

John glided forward on his knees in the shallows, hoping for a closer look at the white flag of the adipose fin on Sherlock's lower dorsal tail. It was as delicate as a woman's handkerchief, shorter than all the other fins and ruffled like lace. It didn't even look like it could move of its own accord –- pure decoration. 

Sherlock's tail reminded John very keenly of some beautiful ornamental koi he had once seen in a garden done in the Japanese style. He had only been in the garden for a few moments, delivering luggage, but it had been enough to see the striking fish in the pond.

John stood up. Sherlock's silver eyes tracked him.

“Can...” John started and stopped. He had not thought this through. His hands twitched at his sides.

The vain creature noticed.

“Can...?” he prompted.

John flushed a bit. “May I touch your tai- er, body?”

Sherlock smirked. “Mine own _tail_ , John Watson. Call it what it is.”

Then, Sherlock gestured magnanimously down the length of his own body, rotating onto his back to watch John. John pulled himself up until he was perched next to Sherlock's much longer body on the rock. This close, he could see the fine texture of each scale. He placed his hand on Sherlock's flank and stroked down.

It felt like interlocking mosaic tiles beneath his callused palm. Sherlock's cool fingers ghosted over John's neck, and John flinched.

“What's this?” the merman wanted to know, gesturing at blush of John's skin. “Does your own kind change color, like an octopus?”

“No,” barked John. “We, um. That is, when... it's a physiological response.”

“To what?” Sherlock wanted to know.

“To...” _arousal_ , thought John. What he actually said was, “...embarrassment, or surprise.”

Sherlock hummed thoughtfully.

John reached for Sherlock's caudal fins. They seemed to be the safest bet. Sherlock obligingly twirled them closer, and with a wet _splap_ a heavy curtain of skin fell right on top of him. John snorted a surprised laugh. The fins were warmer than other parts of the merman's body, the skin rich with blood vessels. Water from Sherlock's gossamer fin sluiced down around him.

Playful, John used the back of his hands to ruck up the fabric-like fins, which were rubbery and much hardier than the impression they gave floating underwater. He looked out from beneath them at Sherlock. 

The creature looked decidedly amused at John's antics.

“You... er, is your kind warm-blooded, like mine?” as if to demonstrate, he placed the flat of his palm on Sherlock's lower abdomen, wanting to share his heat.

“Somewhat. I have dissected many creatures -– tuna, mackerels, and what your own kind call white sharks. They are capable of moderate thermoregulation, like mine own people.”

John's hand stood out against the marble skin of Sherlock's belly, a brown silhouette in snow. The merman made no move to buck John off, although the large gill slits on his ribs cinched closed. John tapped the groove between Sherlock's abdominal muscles with his fingertip.

“You have no navel,” remarked John.

“No what?”

John scooted farther up on the rock. Sherlock did not move to make room, and the sailor was forced to lean against the weight of his tail.

“A _navel_ ,” John explained, shrugging out of his shirt without a stitch of self consciousness.

The air felt refreshing on his bare torso. A flat leather pouch hung from a thong around John's neck, hugging close to his throat as dangling accessories were a hazard for sailors. He never took this off, and actually had a white tan line underneath the crude necklace.

John knew without looking that his upper body was thick with working-class muscle. He did not possess a lean swimmer's physique, like Sherlock. John's skin had been sunburnt so many times that it was brown as a nut, now, and in stark contrast to his sun-bleached hair. A tattoo, long since faded by the sun, smudged the skin of his bicep. John's shoulder muscles were ropey and thick around his neck, pectorals tight, arms sculpted by a combination of his early years as a navvy and life aboard a frigate.

John's body was small, and in another world might have even been delicate. But a lifetime of hard physical labor had taken its toll. John had a reputation for being able to take punches, unflinchingly, that would have sent men twice his size to their knees. John also had a reputation for being able to _throw_ punches that, to hear drunken boasts, would send a man flying three continents away.

Three Continents Watson leaned back on his arms on the edge of the rock. He felt the subtle shift of Sherlock's tail against the fine blond hairs on his forearms. He smiled, for he could feel Sherlock vibrating with curiosity.

“I'm going to touch you,” said Sherlock. It was not a question.

John's pulse leapt in his throat, and he tried to nod, but Sherlock had already flattened his webbed hand in the middle of John's chest. He spread his fingers slowly open in the wiry gold hairs there, testing their texture. He seemed intrigued by John's body hair. Sherlock stroked down John's belly and dipped a claw gently into the fold of his navel.

John instinctively sucked in, pulling his navel away from the tickling touch with a huff. Sherlock glanced up at him and smirked. His hand slid back up again and found the flat disc of John's nipple instead. He gripped it gently between the pads of his finger and thumb, careful to tip his claws back so he did not scratch, and twisted carefully. John arched into the touch and suddenly his cock was filling in his trousers. He hadn't been expecting _that_. 

Sherlock asked breathlessly, “What are _these_?”

Struggling to keep his tone unaffected, John said, “Nipples. Women feed babies with them.”

“Ah. Dolphins do this, also,” Sherlock acknowledged. “You are male. Why do you have these?”

 _That's... a good question_. John shrugged. “They're useless on men. Not sure wh- _hooo_ , ah, Sherlock...”

Sherlock was tugging on his nipple. John covered his budding arousal with a cough, bowing his chest away from the merman's inquisitive fingers. “All right, that's enough of that!"

Sherlock had already moved onto the next biological landmark that interested him. His hand settled on top of John's scar. John felt a splinter of phantom pain and he frowned, but the merman was ignoring him, squinting at the scar. If Sherlock had been another man, John probably would have just tossed him into the ocean like an unwanted sack of produce. But Sherlock was much too large for John to lift, and possessed of sharp claws and teeth.

John was aware of their size difference quite keenly in that moment. So he held still with tense shoulders.

Sherlock asked, “What weapon caused this?”

John had to resist the urge to grip the leather pouch around his neck. “A bullet. From a rifle.”

“A rifle?”

“Yes,” John said crisply. John's scar  was a deep indent in his shoulder, a starburst of spidery lines spraying out from the point of impact. The sun had turned the entire affair shiny and silver as a sixpence. Infection had ravaged it and nearly claimed his life. The merman pulled him forward to look for an exit wound, but there was none, for the bullet was unable to penetrate fully, and had become lodged in the deep muscle. A piece of John's shirt had been punched into his body with the bullet, and caused the terrible infection. 

As usual, John was lucky to be alive.

John got the sense that Sherlock was not done with this topic, not by half, but the merman seemed to sense that John had no patience for questioning in that vein. Sherlock tugged at the pouch around John's throat instead, eyes gleaming.

“And this?”

“It's _personal_ ,” John said shortly, and injected steel into his voice. Sherlock made a complicated dolphin clicking sound in the back of his throat.

To distract him, John scooted until his back was facing Sherlock. The movement felt good on his aching muscles. Fantastic, actually.

John listened to his body's urge and leaned forward to stretch his arms over his head, leaning out above the water and holding the position until his muscles burned. He felt his linen trousers pull with the movement. He felt Sherlock's cold hand settle proprietarily on his lumbar dip.

John froze. The icy points of claws traced oh-so-delicately down the dip of John's spine, pouring like water into the cleft of his arse where it was just barely exposed.

“Fascinating,” Sherlock said, baritone so deep that it rumbled through his hand on John's arse before it reached sailor's ears.

John's cock was almost fully hard now, and he refused –-  _he just refused_ , to think about that. When John became uncomfortable, he distracted himself, or others, from the situation at hand. John did this now by promptly falling back into the crystal waters below. He let himself sink to the bottom and curled so that he was looking up through the water at the skylight. The sun must have set sometime when they were talking, because the quality of light in the grotto had changed once more, purpling with the advent of twilight.

He held his breath and stared unseeing into the distance. He reflected on the chaos of the night before. He could hardly believe how he had come to this place, alive but spirited away by a merman.

It was incredible. How many other human beings had ever met a merman, and lived to tell the tale? If John looked at it that way, he was fortunate. His hand settled around the leather pouch at his throat, feeling the comforting weight as he bobbed slowly to the surface.

When he broke, Sherlock was gone.

John quickly stood. There was a wet spot on the first step where the merman had been reclining, and he could see small gravel and dust had been swept off the edge where a great body had slithered into the water once more. Sherlock had apparently glided out of the cave like a living shadow while John had his underwater reverie.

John shook his head in amazement.

“Sherlock?” he tried calling anyway.

His voice echoed, unanswered; he was alone.

Well. Who knew how long that would last? John sighed, wishing he wasn't dependent on the merman. If John thought too much on whySherlock wanted to keep him isolated in the grotto, he knew he would not like the answer he found.

For now, he decided to work out his sleeping arrangement. The cave was temperate and humid, with only the occasional whistle of sea wind. It didn't seem likely he would freeze to death in the night -- Mediterranean waters were the most pleasant in the world.

It seemed that the only moderately comfortable looking place to rest was right back out on the flat rock.

John grabbed his dry shirt off the first step of the ziggurat and waded out to it. The fish carcass was missing, although there was a grease stain on the rock where it had lain. The conch was missing as well. John climbed up onto the rock and rolled his shirt up for a primitive pillow. He lay on his back and arranged himself in that cautious way one does when one foresees an uncomfortable night's sleep.

John stared out the skylight at the rising moon and let the lapping of the ocean outside coax his restless mind to slumber.

 

**Notes for the Chapter:**

> Comments are the fish flakes in my tank. They keep me alive while you ignore your promise to your parents that you would feed me, and change my water, and keep the door locked so Mittens can't torment me. I hate Mittens.


	3. The Perfect Cage

**Notes for the Chapter:**

> Thanks to JP and Dee for beta'ing, as usual! <3

The next morning, John woke with the sun.

He slipped off the flat rock waded outside. The sun was an unhatched yolk on the eastern horizon, hazy with the heat of what was promising to be a real scorcher. John squinted in the half light and bent his knees, frog-swimming slowly out into the lagoon. There was no sign of Sherlock, so John took advantage of the merman’s absence to examine his surroundings. It was low tide. He climbed up the gravel shoal that enclosed the still waters of the lagoon, sending a slide of wet stones as he went. The endless blue of the ocean was more familiar to him than his own mother's face.

He smiled slowly.  _I survived._

John meandered down the length of the shoal, letting out a low whistle of awe at the size of the grotto's gaping mouth. Pink dawn light striped across the black rocks; ancient layers of algae and barnacles studded its surface like marine jewels. The grotto was nested inside a rocky outcropping that protruded like a broken finger from the rest of the island. John hadn't yet explored the cave, but he would bet a groat the only way to reach the more habitable side of the island was by sea. John wondered if he was a strong enough swimmer to make the trip.

He surveyed the waves.

 _There_. The subtle miasma of a rip current peeled out from the shoal on which he stood. At least, it looked like a riptide on the surface. John's experience on the needled at him, told him that something was not quite right about that current, and the longer he looked the more he began to suspect that what he was seeing wasn't a riptide at all, but something new and unquestionably deadly. 

John reached for the pouch around his throat. The damp weight of the leather reassured him. Pushing down a surge of anxiety, John waded back into the lagoon and paddled to the eastern shoal. He climbed onto the gravelbar and repeated his survey.

“What the devil?” John couldn't believe his misfortune. 

There was a second current formation on the east side, identical to the first. If John tried to access the main portion of the island via the most efficient sea route -- skirting the coast, he would be sucked away, dashed across undersea rocks, drowned, or even just flung out into the middle of the ocean with no hope of ever making it back alive. After a moment of consideration, he supposed that an excellent athlete might swim straight out of the lagoon and into the open ocean, going out so very far the not-riptides would no longer pose a threat... but what a trial for someone without fins!

It was more sensible to wait until high tide to see if the water would change. _  
_

Sherlock had chosen the perfect cage for him. Rage and nausea suddenly roiled in John's gut, threatening to make him retch. He bent over, putting his hands on his knees for support, and breathed deeply through his nostrils to quell the skittering panic. The gulls cried overhead as though they were mocking him --  _here, look at me, I can fly wherever I wish and you are bound to that little sea cave._

After a moment, John straightened up. Wallowing in self-pity never did a man any good. He had survived the disastrous storm, and he had to believe this imprisonment was temporary. He believed there would always be another solution if he just kept his wits about himself. He could not succumb to his fear. And then John’s distracted hindbrain mistook the dark shape of Sherlock in the water to be a shark. He went stiff as a plank.

Sherlock sailed in, shaking wet ringlets out of his face. John pressed his hand to his chest as though the action would smooth down his stuttering heart. Sherlock had the pink conch tucked up on his shoulder, where it would not become contaminated with seawater.

“John. You are awake earlier than I expected,” It didn't seem fair for the merman to be so effortlessly cool in his greeting when John clung to the precipice of calmness through stubbornness alone.

Injecting a calm he did not feel into his own voice, John replied, “Yeah, well. Some habits are hard to break. This is a right lie-in, for me.”

Then, to dismiss the subject, John turned and swam back inside the grotto. The back of his neck prickled self-consciously where he imagined the merman was watching his retreat. It was entirely unnerving how silent such a big creature was in the water -- it seemed mermen only made sounds when they wanted you to hear them. John climbed onto the flat rock, and Sherlock drew up beside it and placed down the conch. John was glad to quench his thirst from it. 

Sherlock watched him drink.

John wiped his mouth, which only succeeded in replacing fresh water with salt. “Where did you go last night?”

The merman swirled in a lazy circle around John's rock. “Hunting.”

“What do your kind eat?”

“Fish. Primarily.”

John knew it was a bad idea to voice his next thought. He knew it, and he still said it. “And humans.”

“Yes. When I can find them,” Sherlock suddenly surged out of the water and held himself up on the edge of the flat rock. John skittered back on his hands and knees like a startled crab, an ember of anger flaring to fire in his breast.

“Why haven't you eaten me, then?” he snapped, clambering to his knees in an effort to lessen their height difference. 

Sherlock gazed evenly at him. There was an invisible thread between human and merman, a hazy pressure that only the two of them could feel. John wanted to push his hands through this unseen miasma, wanted to tangle his fingers in the riot of wet sable curls and explore the texture of Sherlock's lips with his teeth. He wanted to see if Sherlock would bleed. John licked his lips despite himself. Sherlock's gaze dipped to John's mouth.

But then John's stomach gurgled and the tension broke. Sherlock was not a particularly expressive creature, but John saw the faint crinkle of amusement around the merman’s eyes. He slid like an arrow back under. “Perhaps it's time for _you_ to eat. I saw a school of tuna not far."

John scrambled to the edge of the rock. “Wait.”

Sherlock looked over the wet porcelain of his shoulder at John, who said: “I want to explore the island. Can I go there?”

“I do not know. _Can_ you, John Watson?” Sherlock asked unkindly, wrinkling his nose into a patronizing sneer.

John did not rise to the bait. He smothered the little worm of panic in his belly. “I would really like to look around the island, Sherlock. I won't try to escape.”

That was a lie.

If John saw an avenue to escape, he would take it. Living out the rest of his days under Sherlock's webbed thumb was not at the top of John's list. The likelihood of finding a way off the island was slim, but he had a better chance of coming up with a plan if he was not confined to the grotto. Sherlock's silver eyes drifted slowly from John's face down his body. They lingered on his legs. John held firm under the scrutiny.

“No," Sherlock said finally. “The island is forbidden to you. If you go there, I will kill you.”

With a slap of his ink-black tail, Sherlock vanished under the water.

~  ~

Sherlock was gone for hours.

John sat sadly on his rock and stared through the skylight as the sun climbed and delivered on its promise to bake the world. At first he sipped the drinking water in the conch and awaited Sherlock, feeling waterlogged and anxious. But as the hours passed, so did John's patience.

“Right. That's it.” John hopped to his feet.

He would not sit on the rock all bloody day. He would explore the deeper reaches of the cave. He had been putting this off because he was wary of incurring his captor's wrath. Well. Sherlock could just be wrathful. John couldn't be expected to sit docile and wait all day.

John left his shirt- _cum_ -pillow on the rock, waded to the stone steps, and began the climb. He was glad of his upper body strength, for one of the ledges was taller than John’s arm span, and required leaping like a squirrel to catch the edge. The air warmed as John scaled the dripping stones near the ceiling. John had to stop and catch his breath when he made it up onto the last platform.

The sea cave spread out below, a beautiful circle of ocean around the flat rock illuminated well by the hole in the ceiling.

Low down, near the ground, was a horizontal crack in the rock curtain; a crawl space. John supposed he might fit through it, and he got down on his belly and shimmied into the darkness. The stone was chilly, and his nipples tightened where they brushed it. Hoping that the rock formation would not choose that time to cave in upon him, John felt his way blindly through the slender chasm --

and nearly fell off a sudden drop on the other side.

He cried out in terror, arm swinging out into the open black. The sound of his own startled shout echoed off of some distant wall. He drew his flailing limb back in to curl protectively against his body, deeply unsettled by his distorted perception in the gloom.

 _Maybe exploring this cave wasn't such a good idea_ , John thought while he waited for icy terror to recede. But the cave was not as dark inside as it seemed, for in a few moments John began to make out murky shapes, a visual mosaic that eventually described a bubble-shaped room. The cliff he had almost fallen off of was not actually a cliff at all, but merely a sharp shallow drop that ended in a stone platform, mirroring the side which connected it to the grotto.

Feeling silly, John dropped his legs over the ledge and stood, proceeding with his hands over his head so he didn't brain himself on any low-hanging stalactites. Spears of dusty light threaded down from what must have been more skylights in the cavern ceiling. To the gulls, John figured the rocky outcropping probably looked like Swiss cheese; pocked with holes. A natural stone bridge stretched out into the glass-still waters of a deep cave lake.

 _Blimy._ John picked his way across the bridge, which brought him out into the middle of the lake before it abruptly terminated in an underwater cliff. John squatted to peer at his own reflection in the glassy black water. John saw his own face stare back; expressive mouth slack with curiosity, crow's feet of good humor still dancing at the corners of his cornflower-blue eyes. A shock of fair hair stuck up in a ruffle on his head, spiked by salt. John shook his head and reached into the glassy stillness, intending to wet smooth his hair.

But the moment John touched the water, it [lit up](https://www.youtube.com/watch?v=T2xh9-UPSlU), blue light flowing outward from his fingers.* As quickly as it happened, the water turned black once more.

John tapped the water again just to see the bright blue eruption. He laughed under his breath in awe. Then John slapped his hand on the water with undisguised delight. Arcs of blue liquid splashed up, roiling in the waves he created, glittering against the velvet backdrop of the dark cave and casting John's body in an ethereal blue light. He held his hand to his face and stared, seeing tiny sparkling forms winking out in the water.

“Incredible!” John said, and his voice shattered the stillness of the cave. Emboldened by the sound of his own voice, John spoke aloud to himself. “I wonder how deep these waters go.”

John cast about. He found a pebble not far from him and stood, pitching the it into the lake. It struck and immediately the water reacted, lighting up in a spiraling caress of blue as the pebble sank.

And sank.

And _sank_.

A boyish thrill hummed through John as the pebble disappeared from sight, bouncing off of some unseen rock on its way into unfathomable depths.

“Blazes,” whispered John. He clutched the pouch around his neck with both hands. This lake was unlike anything John had ever seen, or heard of in his life. It seemed like the sort of place naturalists would be interested in knowing about, and John resolved that if he ever made it off of Sherlock’s island that he would tell the world about the lake that glowed.

John entertained the idea of staying in this cave for a few hours, if only to make the merman think that he had somehow escaped. There was no way that Sherlock knew about this hidden lake -– no way that the merman, for all his impressive upper body strength, could have climbed the steep rocks. And even if he could get up the ziggurat rocks, Sherlock would never be able to fit through the secret entrance.

“This is my place, now,” John told the lake.

The lake was still. 

“I might be going a bit mad,” John said, tapping the pad of his foot against the water to make it light up. First being swept off his ship, then being absconded with by a merman, and now water that glowed. What was next? His grumbling stomach encouraged him to return to the grotto after all, and he climbed carefully back through the gap and down the steps until he sat with his feet in dangling in the clear water, which seemed plain in comparison to the light-up lake.

He did not have to wait long. A large, dark shape sluiced through the waters of the lagoon, and then into the grotto itself.

“John Watson,” greeted Sherlock. He came close, and John saw that a tuna was tucked beneath his arm.

“Finally,” John couldn't help but say. It was rude, he knew, but so was keeping a bloke captive.

Sherlock just smirked. He rolled the fish onto the rock, belly up, and as John watched, Sherlock flayed it open with his claw. John's stomach rumbled in pleasant anticipation. He made to approach the promise of lunch, but Sherlock interrupted by coming to him instead. Sherlock folded a fatty slice of pink meat in his fingers, and held it out to John. Clear blood dripped into the webbing of his hands.

John reached out for the morsel. Sherlock pulled his hand away.

“Oi! What are you playing at?” growled John. “Tormenting me again? I thought we were beyond this.”

John actually was not sure if they were beyond this, but he hoped that his words would inspire Sherlock to greater civility. The merman was silent, pale face inscrutable. He offered the fish to John once more. The motion was deliberate. Slow. John's throat went dry with understanding. Shame threatened to bloom inside of John, and the sailor projected his fiercest glare at the merman.

Sherlock's mouth curved in a slow, knowing smile, the kind of smile that said  _I have all day, and you are hungry, and we both know how this ends_.

John weighed whether it was worth getting into collie shangles with Sherlock about this. He supposed that he had done more humiliating things for food in the past. Hunger won out. Snorting to cover his embarrassment, John leaned forward and let his lips part in slight receptivity.

Sherlock's smile widened and exposed the pointed tips of his pointed teeth. He brought his hand closer to John's mouth, and John leaned forward to delicately pick the fish out from those gleaming white claws. The spicy, buttery rich flavor burst over John’s tongue and he closed his eyes so he didn't have to see the merman's smug face. 

John wanted to be stubborn, he really did, but hunger had a way of dulling a man’s will. He used his teeth to pluck another piece of fish carefully from Sherlock, smothering a not-entirely irrational fear that Sherlock would sink those pale hooks into the delicate skin beneath his eyes and rend. As soon as John swallowed, Sherlock was there with another fold of tuna meat, nudging it against John's lips. John opened up. At one point, he took issue with the pleased expression on the merman's face, enough to deliberately bite the chilly pad of Sherlock's finger -- and this John regretted doing, for Sherlock's hand immediately tightened around his jaw. 

Claws pressed lightly into John's face.

Sherlock's gills were flexing and his expression had gone somewhat feral. John was reminded that, despite his appearance, Sherlock was not human. John dipped his tongue out to gently lick some of the blood off the webbing between Sherlock's fingers, and the merman's ear fins twitched.

 _Oh, why in the heavens did I do that?_ John thought, feeling very base and stupid although Sherlock was looking at John as though he had done something interesting. He also seemed to be emitting a soft clicking noise in the back of his throat, so faint that John could barely hear it. Uncomfortable and no longer interested in being fed, John resigned himself to a scratched face and pulled away. Sherlock let him go.

John cleared his throat, not knowing what to say, and ended up staring at the place where Sherlock’s torso melted into black scales.

“I am not finished with my questions for you,” Sherlock said finally. This close, his baritone voice was especially resonant.

Sherlock had been propped up level with John during his lunch, using his tail as a ballast. Now he sunk back under the shallows and submerged his neck gills. John splashed his toes awkwardly in the water where they hung. The rock step was hard under his arse; pins and needles prickled in his calves. “Oh. Well. I promised you I'd answer, so -”

“Yes, you did promise,” interrupted Sherlock hurriedly. Then: “Are your own kind exclusively day-time?”

“Day-time -– oh, uh, yes. We sleep at night. What about your people?”

“Males of my own kind prefer the twilight hours, and will sleep during the high sun and moon. Females are nocturnal.”

John was curious about this. “Are your womenfolk so different?”

Sherlock was staring at John’s legs where they hung over the edge in undisguised fascination. He answered distractedly, reaching out to stroke his hand over the hairs of John's calf. “Yes.”

John waited for elaboration, but nothing was forthcoming.

“Take off this covering,” said Sherlock, pushing the hem of John's linen trousers up. You'd think the merman had seen Victoria's own Sovereign Orb, with the way his eyes lit upon the revelation of John's bony knee. 

John swallowed. “I'd rather not.”

The merman scowled. “You promised. I let you touch mine own body.”

The sailor squirmed at the cool touch on his knee, deliberating. Sherlock had let John touch his tail, but that, that was different. The merman was... beautiful. And he knew it. Sherlock was the perfect marriage of strength and aesthetic, of practicality and excess. John was just a human. In comparison, he was small, swarthy, and depressingly well-adapted for a life on land.

John reverted to a ploy that had worked before. “Don't you want to test how long I can hold my breath under the water?”

“I wish to observe your own body in its entirety before conducting further experiments. Now remove your own coverings, they offend me.”

To demonstrate the offense he took, Sherlock sneeringly lifted John's dangling brace strap and let it fall back onto the rock with a _plap_. John sighed.

“Stand up there so I can see you,” added Sherlock, swimming away to give John room.

 _I must be barmy._   John got into the water so he could climb onto the flat rock that served as his bed. The sun had baked such heat under his bare feet that John had to shuffle in place. John stalled for time by drinking out of the conch. He looked around for some other means of prolonging his modest state, but there was nothing for it. He was going to have to disrobe.

The merman circled the rock below, submerged.

John peeled off his soaked trousers with difficulty, and it was a graceless operation to divest himself of his undergarment. His clothing seeped a dark wet stain across the stone, and John focused his gaze resolutely on the spreading water below as he stood, nude as the day he was born, alone upon the rock.

Sherlock scared the devil out of John by suddenly hurtling out of the water and landing in a graceful push-up on the rock with his enormous tail spilling heavily over the lip.

" _Tarnation_!” cursed John. He stumbled back in surprise and completely overshot. John felt air rush in his ears the split second before he hit the water and went under with a colossal splash. The water enveloped him and he flailed gracelessly under it.

He rose spluttering.

John glared up at Sherlock where he was perched above on the rock, and opened his mouth to snarl something unpleasant. But Sherlock was shaking; his gills fluttered and he was expelling little huffs of air, nose wrinkled. John realized, with no small measure of surprise, that the merman was _laughing_.

“You gave me such a fright!” John admonished finally, paddling his arms slowly for balance.

“Evidently,” chuckled Sherlock. It seemed that even mermen were capable of laughter, although to John's ears it was a reserved sound. He scraped his claws over the lip of stone. “Swim, John.”

John found this request much more agreeable than standing nude on a rock. He kicked off the sand and made his way to the cave mouth with a powerful backstroke before Sherlock could get more specific in his demands. Sherlock's head turned to follow John's progress, an amused little tilt to his mouth. John ducked out of the shade of the sea cave and into the blinding afternoon sun. The light reflected off of his white-blond hair where it slicked to his skull. He took in a breath and dove under.

John liked swimming.

He was reasonably good at it -- unlike many of his peers, who, despite working on a ship, did not know how to swim. The water was deeper in the lagoon, perhaps five or six feet compared to the three or four in the grotto. John skated along the bottom.

Sherlock appeared in his peripheral vision, a dark serpent in the bright water. John knew Sherlock was observing him as he swam. He looked over his shoulder at the merman and flashed a grin, a bubble of air escaping. Something about the pressure of the water on his body was comforting; John's self-consciousness fled and he rolled to look up at Sherlock.

Sherlock's gaze immediately went to his groin. _Oh, of COURSE he would look there first._  John dropped his hand to his own hip and crooked his finger at Sherlock in an 'eyes up here' gesture. Sherlock glanced up at John, and then that pale gaze dropped right back to the prize.

John rolled his eyes and surfaced to breathe just as his lungs began to burn. This time, when John dived back into the cool sanctuary of the ocean, Sherlock had drawn nearer and John was blindsided by how beautiful the merman looked while in his element. His scales gleamed like interlaced black mirrors and his white fins swirled and rippled like sails unfurling in a good wind. John was struck with a pang of homesickness.

Sherlock circled John gracefully, and John couldn't help but to reach out and stroke along one of the sheets of fabric-like skin when it flowed by. He grinned at Sherlock, who mirrored the expression. He let himself sink to the bottom, legs criss-crossed, and paddled his arms to stay vertical. Sherlock floated in front of him, and his smile transformed his face from living marble to something much more human. It made him look approachable. John reached out and felt the webbed cartilage of Sherlock's ear. To his shock, the merman made a clicking noise that was audible even underwater, and thrust his face into John's palm.

 _He’s like a great bloody cat_! thought John, rather in awe.

Sherlock’s mouth was parted, and as John watched, Sherlock's tongue darted out to stroke shiny slick across his plush lip. John's pulse skyrocketed and he felt a regrettable need for air. John ignored that in favor of carding his hands through Sherlock's floating curls. Sherlock looked coquettishly at John through a lace of black lashes. John found himself leaning forward unbidden, despite the burn in his lungs --

A tiny silver fish darted suddenly between their faces and broke the spell.

John laughed in surprise and in so doing depleted his remaining air. He made to push off the bottom, but Sherlock’s monstrously strong hands settled on his shoulders, forcing John to stay on the ocean floor.

John seized Sherlock's hands and tried to wrest him off. He convulsed, thrashing wildly, but the merman was too strong, and John tried to remember how he had survived this monster's capriciousness the first time. It went against every biological imperative he had, but John yielded, going still and squinting desperately through the cerulean gleam into Sherlock's eyes.

_Why are you doing this?_

Sherlock's pupils had transformed into the w-shaped squiggle of a cuttlefish. Sparks danced behind John's eyes. He slid his palm up the length of Sherlock's arm where it held him down and cupped his cheek. His fingers were going numb, but John kept his touch reverently soft. Something about the gentleness in this action seemed to rouse Sherlock. He abruptly seized John underneath the arms and launched them both from the ocean floor to the surface in one brain-rattlingly fast motion.

Sherlock nearly dislocated John's arm in his haste, but John was too grateful to have air again to complain. Sherlock supported him above the surface as John wheezed. Dimly, he was aware of Sherlock making a tender little crooning noise, and soothing those clawed hands down John's heaving chest.

John had no words. What could he say? Sherlock was clearly insane. The creature did what he wanted with no regard for John's safety. The merman was dangerous, and matter how human Sherlock looked, he was still a monster. A beautiful monster.

This latest stunt solidified John's resolve to find some way to escape, and to the best of John's understanding, the other side of the island was his only chance. He floated in the cage of Sherlock's arms, feeling the slow, powerful undulations of the merman's giant tail, and began to plot.

~  ~

_*John didn't know this, but dinoflagellates in the lake water reacted to stimulation, illuminating in a spray of vibrant cobalt blue when disturbed._

 

 

**Notes for the Chapter:**

> The next chapter is where certain tags become truly relevant, so please reacquaint yourself with them if you are under the mistaken impression the sex scenes will be pearly, romantic purple prose. (That doesn't happen until later.) In my world, merfolk are _dangerous as hell_ and feylike in their worldview. Sherlock is not a human with sexy fins. He's a _monster_ with sexy fins. It's going to take some time for John to tame him.
> 
> That said, I hope you enjoy! See you next Sunday!


	4. Crude Experiments

**Summary for the Chapter:**

> _“What does a kiss mean?”_

**Notes for the Chapter:**

> Happy Sunday update!  
> Tag relevancy: " _moments of dubious and awkward interspecies consent_ ". In real life, you should always have a discussion with your merman lover before you have any kind of sex with him, exchange a sexual history, discuss prophylactics, and generally do all the things normal folks do when embarking in a new sexual relationship with a mythological creature.

Sherlock never actually apologized for almost drowning him, but he did  give John some space.

The lack of apology bothered John because it was difficult to refrain from impressing human ideals upon Sherlock. He oscillated between feeling a sense of kinship with the creature, and fear when Sherlock demonstrated just how inhuman he was.

Sherlock brought him more fish, but John refused to eat, and the merman did not insist on hand-feeding John again. That was good. If Sherlock insisted on feeding him in this state, John could not be held accountable for his actions. He imagined the satisfaction of biting into the merman's pale fingers until they bled. John wondered what color a merman's blood was. Was it clear and watery, like a fish? Or was it the red wine of a man?

If Sherlock tried to drown him again, John vowed to find out firsthand.

~  ~

John woke the next morning in a terrible mood; the rock was hellishly uncomfortable. On top of that, Sherlock had hidden his trousers and unmentionables somewhere, leaving John to sleep naked. His stomach was cramping with hunger, the stubble growth on his face itched, and the sky was looking distinctly like rain. Cool air gusted into the cave and brought with it the ozone flavor of an impending storm. 

“Your claws are useless,” observed Sherlock from where he was fixated on John's bare feet. He sounded a little disappointed.

John unleashed an exasperated groan and sat up, glowering at the merman where he floated half out of the water in order to examine John's toes. How long had Sherlock been staring at him while he slept? Was there no concept of privacy in merfolk culture? Or was it Sherlock, specifically, who refused to acknowledge personal space? He may not have known Sherlock for long, but John had a hunch that it was the latter.

“Now listen here,” started John, voice croaky with sleep. He was interrupted when Sherlock tossed an object at him, which he caught reflexively. 

It was a green coconut. John was familiar with them –- on one of the first ships he had worked, the sailors would collect coconuts on shore leave and bring them back on board. If a crate of them spilled into the sea, they could be carried along for miles before landing on some sandy shore and populating it, although John had never seen one in the Mediterranean before. _What a curious island_ , John thought, and quite forgot what he had intended to say to Sherlock.

John migrated over to the first ziggurat step with the coconut. Sherlock rested his elbows on the flat rock and tracked him with his eyes. John did not need tools to open a young coconut like this. Brute strength would do. John cracked the weak end of the fruit against the rock, twirled it in a long-practiced motion, and smashed it again; the coconut began to leak and he held it to his mouth and gulped; he felt the liquid he did not catch splatter down his throat, dripping off his talisman-necklace and down his chest.

Once he had drained the coconut of its milk, John pried his fingers into the chink he had made and the ropey muscles of his forearms contracted with the effort of tearing the drupe open. He glared when Sherlock drew nearer with fluttering gills and blatant fascination.

“I'm still mad at you,” John told Sherlock bluntly around a scoop of coconut flesh.

Sherlock's inner eyelids blinked. “John.”

Hearing his name shaped by that basso rumble made an electric current of excitement zing through John’s body. “ _No_ , Sherlock. What you did was downright rude.”  _Rude? Why the devil did I say that? He nearly killed me!_

Sherlock did not have anything to say to that. “Come into the water, John.”

“Certainly not.”

“Why not?”

“Why the bloody hell do you think?” burst John. “Every time I get in the water with you, you try to drown me.”

Apparently John had made a reasonably valid point, because Sherlock fell silent.

“Although... if you make me a _promise_ , I might be willing to change my mind.”

Sherlock's head snapped up where he had been sinking slowly underwater. There it was, again. That magic word that seemed to mean something to Sherlock. _Promise_.

“What promise?” the merman asked carefully.

“That you will not drown me.”

“I won't promise that,” said Sherlock.

“Then I can't get into the water with you."

Sherlock scowled. John looked evenly back at him. Outside the relative shelter of the cave, the sky fulfilled its promise and began to rain. John eventually won the staring contest.

“I promise,” said Sherlock.

John smiled in relief. He slipped into the water, and it wasn't until Sherlock's presence swarmed up on him that it occurred to John that he probably shouldn't have permitted Sherlock to be so vague, for the merman stayed underwater entirely in order to coast his hands up John's naked thighs. To John's alarm, his cock twitched with interest a moment before a huge hand cradled his cock and bollocks with unexpected delicacy.

John behaved like any man would if his private bits were suddenly grabbed: he shouted in surprise and held very, very still. Sherlock didn't even have the decency to be above water so John could tell him off or perhaps have a nice conversation about private bits and civilized behavior. It was all happening too fast for John's liking and he plunged his hand below to seize Sherlock's wrist with bruising force.

They were rather at a deadlock.

Sherlock refused to let go of John's intimate anatomy.

If anything, the merman seemed a little titillated by John's discomfort.

John stared down at the dark cloud of Sherlock’s curls where they drifted in the water. He couldn’t see the merman’s face, couldn’t determine what Sherlock might be thinking. The lack of eye contact rattled John more than a strange bloke having off with his todger. Once again, John could only yield and hope that mercurial Sherlock would lose interest in his unmentionables soon. John summoned bravado that he did not really feel and released his grip, heart thumping so quickly in his chest that he was certain the merman could feel it underneath his skin.

John was more afraid now than he had been when Wylie Clegg went on the ran-tan and held a knife to John’s jugular with no provocation. At least Wylie had been willing to listen to reason -- he and John had grown quite close after that incident, actually.

But Sherlock? John was not so sure diplomacy would have any effect. Sherlock did not have the excuse of being into his cups; the merman just  did what he wanted, when he wanted to do it. A secret thrill shivered through him. The cup of Sherlock's hand gentled, and he stroked the back of his fingers down John's flaccid length curiously, rolling the vulnerable head of John's penis into the webbing between his fingers. Soft as he was, John just found the sensation uncomfortable.

Sherlock surfaced in order to speak. “This is your genitalia.”

“Yes,” John confirmed briskly.

Sherlock nodded. He dipped back below.

“Now, wait just a minute,” said John rather breathily, but Sherlock was back to exploring, and seemed particularly interested in John's body hair. He twirled his fingers in the dark blond curls at John's groin. Despite his fear, or in part perhaps because of it, John felt the first threads of cautious arousal begin to unspool in his belly. Sherlock lifted John's bollocks on the backs of his fingers, looped his palm around John's cock and rubbed down the hardening length slowly. His touch was precise and scientific.

If Sherlock had not been such a heart-rendingly sensual creature, John might have been able to think sufficiently ugly thoughts to keep his affair disinterested. As it was, John couldn't help but notice the lean white line of Sherlock’s back under the clear water. John felt the quality of Sherlock’s touch on his cock shift from clinical to personal, and the merman used strong hands to part John’s legs into a wider stance for better access.

Sherlock did something, there under the water, to his hand and when he returned it to John's cock it was slick and John pushed his hips into the motion, brain not quite caught up with his body. Sherlock worked John to hardness, pulling his slick hand up and down the long heft of John's cock. Pleasure and anticipation of relief built into the sweetest ache. John was starved for touch, for a release of months of tension and the distracted attention of his own left hand, and he rocked his hips a little and Christ the channel of Sherlock's palm felt like heaven.

“Shhher- _aaah_ …” John tried to sound stern, to get the mischievous creature’s attention, but his voice weakened with the gratification of touch.

Sherlock stared up at John through the water as he milked John's cock with an expression of rapt fascination. John, for his part, was gritting his teeth so hard that the tendons stood out in stark relief on his tanned neck. He was not going to last long.

Well.

John was no shrinking violet. Sitting passively by whilst a lover attended him had never been his habit. With a growl, he grabbed Sherlock’s wet curls and _pulled_ , and the merman hissed as he was manhandled out of the water so that John could claim Sherlock’s plush lips in a bruising kiss. Sherlock’s bicep was hard in the curl of his palm. Sherlock did not seem to know what to do, and his mouth was slack beneath his, but John did not care; he bit that soft lip and pulled, thrusting his tongue through the velvet pout to stroke against pointed teeth in blatant challenge -- and yes, yes John _did_ nick his tongue and the slight sting of pain served only to heighten his pleasure.

Sherlock did not know how to open into the kiss as a human lover would, but his hand on John's cock was slick and tight and John rode Sherlock's fist with violent snaps of his hips until the pleasure built in his lower spine and all the way through his cock, a thickening herald of impending release announced by a startled shout. John folded over Sherlock and clenched his fists white-knuckled in the merman’s black curls, spending in hard pulses with a deep groan. Sherlock refused to relinquish him until he had milked a final and feeble expenditure from John, eyes sharp as silver pins.

John released Sherlock’s tormented lips with a wet pop and he was surprised to find his legs wobbling coltishly.

“Yes, yes... very good John,” whispered Sherlock, supporting his weight with ease. Then, in a hushed voice, he ruined the moment. “Your seed -– it has fertilized this water. Your kind copulates on land, though, I take it? Would you fertilize the female's body by spraying your seed upon her?”

John blinked, still panting, and then he couldn't help it: he chuckled and shook his head. He did not answer right away, but he was glad of Sherlock's sturdy presence in the water while he reconstituted from the shock of having it off with a merman.

“Sherlock. You could have warned a bloke before - before engaging in _carnal relations!_ ” to emphasize his words, John slapped his palm firmly against that narrow chest.

Sherlock seemed to be considering what John said, and the silence was heavy with the weight of his contemplation. John lay back and floated, although Sherlock's arms were still lightly supporting him. He stared at the cave ceiling and drifted in a fugue state, lulled by the sound of the rain and reflecting on just how badly he must have needed a release of tension since he had been swept overboard, for what had just transpired surely took to the top of John's list of mad experiences. It had felt amazing. John felt pleasantly lethargic and some of his anxiety had vanished.

Sherlock leaned anxiously over him to peer into John’s face, and the watery sunlight framed his dark curls in a corona of light.

In that moment, he looked angelic.

“Blazes, but you’re beautiful,” whispered John with a lazy smile.

Sherlock’s eyes widened and he actually flinched in a way he had not when John smacked him, and he shoved John away from him so suddenly that John had barely enough time to close his mouth before he went under. It was unfortunate that John was becoming accustomed to this treatment. He rose with only a minimum of spluttering.

He felt rattled. Almost as much as sex, John loved curling himself into or around his partner after the story of their pleasure had been written. He appreciated the post-coital window, that time of terrible and beautiful intimacy in which two bodies calmed in the scratchy hemp embrace of a gently swinging hammock in the sailors’ sleeping quarters. And despite the surprise frigging, the way the merman had held John after bringing him off had been unexpectedly patient. In that moment, Sherlock had not been so dissimilar from a human lover.

But as quickly as the potential for warmth on the merman’s part manifested, it vanished. The likelihood of Sherlock understanding that John would appreciate a little consideration in the aftermath of their coupling, if it could even be called that, was slim to none.

John clenched his jaw until his teeth slid together. “Why did you do that?”

But Sherlock had turned away from John, shoulders hunched. He was touching his fingertips to his mouth, and a little wrinkle had formed on the bridge of his nose as though he were trying to solve some mystery. John paddled closer, decidedly not thinking about the fact he was probably swimming through his own sexual emissions.

“Oi? Sherlock?”

Sherlock refused to look at John. His neck gills fluttered rapidly and Sherlock vocalized three deep clicks, without opening his mouth at all. In hindsight, John couldn’t say why he did what he did next.

He clicked back. His own human vocal cords were incapable of the volume that came effortlessly to Sherlock, but the sound was otherwise apt. Sherlock’s reaction was immediate: he turned back to John with a questioning expression. After a lightning-quick assessment of John -- was he checking for injury? -- Sherlock relaxed and seemed to collect himself.

“...Why do you do this?” Sherlock asked, stroking his long fingers against his kiss-swollen lips. “This is the second time you have done this to mine own mouth.”

“What, a kiss? That’s hardly an unfair price for access to - to experimentation,” John finished delicately.

“A kiss,” mused Sherlock. He let the sibilance of the word hiss out from between his teeth. “So that’s what it’s called.”

John, still nude, climbed onto the flat rock and found the solid stone a comfort beneath him. He resigned himself to the fact that whatever moment he and Sherlock had shared was gone. John just felt tired and a bit hollow. He tilted his face up into the light rain that threaded through the skylight. He visualized his worldly concerns being washed away with the water down his face.

When he spoke, it was with deliberate calm. “What, Sherlock, don’t your people kiss each other?”

“No.”

“Huh." John didn’t really know what to say to that.

But Sherlock continued. “What does a kiss mean?”

“What does a --”

Oh, _mercy_.

John groaned and put his hand to his face, then pushed it up and through his wet hair. What did a kiss mean? It was not a question the thirty-two year old had ever had put to him before, and with a life on the high seas John was little given to introspection on such a frivolous topic.

After a moment, John said, “Well. A kiss is an expression of sentiment.”

“ _Sentiment_.” Sherlock echoed. His voice dripped with disdain.

“Yeah,” John said. “It communicates passion, romance, sexual attraction -- it… well, it’s just something people _do_. It feels good.”

“Hm. Mine own kind do not feel the need to lick each other’s mouths to communicate. That would be especially inadvisable with females, in fact. I have more questions; you will answer.”

John snorted. “Will I, you damned hurricane?”

“Your own kind does not copulate in the water. So how then would you fertilize the female’s eggs?”

John burst into helpless laughter. Sherlock’s curiosity and intelligence shone so bright and blunt. Frankness was quite a commodity back in London proper, and the Victorian art of hidden meaning and conversational subterfuge was not one John had mastered or was ever likely to. Sailors tended to speak plainly, and John preferred it that way.

He laughed so hard that his sides hurt and John found that laughter was a different kind of release, and went along nicely with the post-coital buzz. Sherlock, who clearly thought his questions legitimate, frowned. He waited until the peals of laughter tinged with hysteria faded to a manageable volume and repeated himself.

“Quite a man of science, aren't you?” smiled John, shaking his head.

“Mine own kind are superstitious of humans. Avoidant. I prefer to work with facts,” Sherlock conceded.

“Well. You don't get a woman knapped by spending on her,” John replied vaguely.

Sherlock tossed his wet hair haughtily. “Then how does your kind fertilize the eggs?”

John flushed deep red. “Look, Sherlock, I don't really want to discuss putting Nebuchadnezzar out to grass with you --” (“ _What_?” interrupted Sherlock, alarmed, but John pressed on,) “-- you've had your little experiment and got firsthand results. Without even asking a by-your-leave, I might add! Where I come from, that’s rude.”

_To say the least._

Sherlock looked like he did not care if it was rude. He demonstrated how little he cared by continuing to talk. “You enjoyed it. You promised to answer all my questions, John.”

“For gentle Mary’s sake. A man gets a woman in the family way by spending inside her body. If God wills it, she becomes pregnant.”

Sherlock gestured to John’s genitals, obscured as they were by his criss-crossed legs. “You put that inside of her body?”

John felt a muscle in his eyelid twitch. “ _Yes._ How does a merman do it, then?”

John’s gaze dropped lower again to Sherlock’s inguen. He was done with being coy about it. John figured he had the right to drop any pretense about being disinterested in Sherlock’s bits after what had just transpired. The two flipper-like pelvic fins hugged close to Sherlock’s body, bracketing a window of uninterrupted scales. Sherlock did not seem to have genitalia at all. John glanced up to look at Sherlock’s face, ready to lock gazes challengingly, but the expression on the merman’s face made him do a double-take.

Sherlock was smiling slowly, and John could see his wicked pointed teeth. John realized this might be a bad conversational path to take, and used anger as his shield while backpedaling furiously.

“Never. _MIND._ ” John grit out the word as two separate sounds, clenching his hands into fists at his sides.

“Never mind? Are you sure?” said Sherlock, and his slow smile evolved into a full-on grin, and he fanned open his caudal fins in the water until they floated like an enormous silver-white curtain. The merman ran his hands slowly up his own body, palms curving to fit the mould of his own scant curves and the lean length of his torso -- deliberately drawing John’s eye to the parts of him that were most human. He drifted around John’s rock, still stroking his own body gently, and said, “How many females have you bred, John?”

The rain stopped at the precise moment John let out an affronted huff. “No. Just, no. We are not having this conversation.”

“Five? Twenty? I really have no basis for comparison in human coitus.”

John turned around on the rock and developed a sudden keen interest in staring out the skylight. He could hear the merman swimming around to face him and he resolutely ignored him. As far as he was concerned, the conversation was over. And when John set his mind to something, there was not much liable to change it.

“ _Joh_ \--”

“Sherlock. Bring me more food, make yourself useful,” John interrupted. Then, not wanting to risk provoking his mercurial captor, he added: “I liked the coconut, by the way. S’just not as filling as fish.”

John risked a glance at Sherlock. The merman had risen out of the water somewhat, propping himself up on the coil of his tail. John braced himself for a disdainful reaction, but Sherlock’s curiosity merely found another avenue.

“Ah. So you prefer to eat meat. I was wondering about that, John. Your teeth are as inefficient as your claws. This I noticed when you bit mine own hand, yesterday.” Sherlock said the last part flippantly, but John’s spine still stiffened anxiously at the memory of the punishing grip on his face for his transgression, and how quickly Sherlock’s touch had gentled when John licked the webbing between his fingers.

John still couldn’t say why he’d licked Sherlock. It wasn’t that the taste of fish blood had been so appealing, but nor was it an intentional plea for mercy on John’s part. John realized in hindsight that the merman might have interpreted it as such. Lost in introspection, John’s gaze poured slowly up the pale column of Sherlock’s throat. The light glimmered on the exceptionally tiny, fine scales that sprayed across the merman’s cheekbones, forehead, and even a thin stripe of black scales down the center of his chin, below his lip. John wondered what the texture of those fragile scales would feel like under the swipe of his tongue.

_Watson. Stop thinking about licking a merman._

Sherlock seemed to hear something that John could not. His eyes, which had been glittering with inchoate mischief, focused on some distant place out on the ocean. Sherlock’s aural fins twitched up ever-so-slightly, wet sable curls resettling around them, and his handsome, alien face slowly contorted into an ugly sneer.

“What is it?” John asked, hushed and straining to hear as well. He heard only the usual ocean sounds.

Sherlock did not so much as glance at him. “Mycroft,” he hissed.

“Pardon?” said John.

But Sherlock did not bother to explain, for he was off like a shot, a cascade of water from his sudden motion spilling up over the lip of John’s rock.

“Oi!” called John reflexively, watching as Sherlock’s dark body sliced out of the lagoon and into the frothy, post-storm ocean. John watched until Sherlock was no longer visible, wondering what on earth ‘mycroft’ meant, and if he was in any danger.

~  ~

John did not really know what to make of what occurred that morning.

He was less offended by Sherlock’s disregard for social boundaries than by the fact that he hadn’t been allowed to explore the beautiful creature in turn. He had been so sure that Sherlock’s interest was purely scientific, but something in the way Sherlock had held him afterward, stroking John’s body like it was a treasure, gave him pause.

John decided that he felt a bit cheated.

He wanted to feel Sherlock’s lips open beneath his, stroke his hands down that lithe body and caress where skin transformed so naturally into scale. He wanted to touch everywhere there was to touch on Sherlock’s mythical body, test if there was any part of the his anatomy that caused John’s attraction to dwindle. Part of John wished that he had been the one to initiate a sexual encounter with Sherlock.

 _You’re an odd one, Watson_.  _Thinking salaciously of a merman who keeps you locked away in his sea cave for naught but to sate his curiosity._

At this sobering thought, John’s mind turned itself once more to thoughts of escape. Sherlock had left him that afternoon to investigate the _mycroft_ he had heard - whatever that meant - and had not yet returned. John made his way out into the lagoon proper to reevaluate his options. The afternoon sky was overcast, and John predicted that there would be more rain that evening. He stood out on the rocky shoal and kneaded his toes into the gravel while he considered the foaming water. It would be stupid to attempt to swim out today. 

If John swam straight out into the ocean from the lagoon mouth, he might be able to cast a wide enough berth to get around that mysterious, deadly current that prevented a direct route to the other side of the island. John hoped the other side of the island had food other than fish or coconuts. Maybe there would be wild boar -- John doubted the island was large enough to sustain an animal like a boar, but his hungry imagination did not care. Would there be fruit trees? Nature’s bounty could not be predicted. John wasn’t in a position to be picky, but daydreaming cost him nothing and helped pass the time.

After a while, John shivered in the open wind. He returned to his flat rock in the grotto to wait for Sherlock.

Sherlock did not come, and night fell and brought with it unpleasant, hungry sleep. The conch was empty and John regretted his naive trust that the mercurial merman would refill it for him. John worried that Sherlock, rather than being negligent, was intentionally experimenting on how long a human could survive without food or drink.

He resolved to escape.

“Tomorrow,” John said aloud. Hearing the sound of his own voice was comforting. “If the weather’s good… tomorrow.”

 

**Notes for the Chapter:**

> A final note, **the story updates on Sundays** unless stated otherwise in the chapter notes. Please check the time stamp on recent chapters before asking me to update it soon, or to continue it: I have already answered that question! Thank you for understanding, my wee dolphins.
> 
> Also, though this chapter depicts a sexual release, it's hardly a satisfying sex scene, at least for me. It’s more of a “Sherlock does what he wants and is a rude fishy git” scene. Proper sex scenes are coming up later. My [tumblr](http://www.jinglebell-fic.tumblr.com) has Sherlock themed things and fic update announcements, in case you dig that.


	5. The Island

**Notes for the Chapter:**

> It has to get worse before it can get better. In which John shows evidence of a backbone. As always, JP and Dee have my snuggliest gratitude for taming this monster of a story for public consumption. Here is a [playlist](http://8tracks.com/jinglebell-fic/riptide-lover) that I listen to while making Riptide Lover. Some of the songs are very relevant to the plot of RL (“Never Let Me Go” by Florence, for example, and the tuvan throat singing by the Bulgarian choir) and others are simply mood music. Please laugh heartily at the faux bodice-rippin' romance cover I photoshopped, that is why it exists.

As it turned out, John’s opportunity to escape was postponed because the next three days saw abysmal weather. He was trapped inside the sea cave that entire time.

John thought he might go mad with boredom.

Sherlock did eventually bring John fish and fresh water, but the merman seemed distracted by the turbulent waves and did not stay long. John resented the control Sherlock held over his meals: since he was brought primarily fish, John had to eat immediately for fear of the meat spoiling. The random feeding schedule made him feel powerless. He stashed the second coconut Sherlock brought him in the grotto like a paranoid squirrel.

Something about the storm encouraged ferality from Sherlock.

The quality of the merman’s energy had been coaxed into a fine vibrato by the ozone wind, and John envied Sherlock his freedom to plunge headlong into the deep. No matter how violent the storm, the ocean was Sherlock’s kingdom. John imagined that having the tools to navigate the dangerous waters mid-storm would be very freeing, and certainly more exciting than stagnating in the sea cave with John. Even the ocean matched his mood, with its volatile dark blue waves.

John tried to entertain himself by going back into the secret cave and splashing in the light-up water, but even that lost its appeal after a few days. Robbed of other stimulation, John watched the roiling clouds and thought obsessively about escaping.

On the fourth day the weather cleared, and that very morning John swam out into the lagoon before he had even wiped the sleep from his eyes. Determination gave him strength. He floated in the clear water and watched the white-hot disc of the sun rise in slow motion. There was no sign of Sherlock.

“Right,” John muttered. Sherlock had stolen his trousers and undergarment, leaving him with only his ragged shirt, which he had opted to tie around his hips in a primitive kilt. John’s hand lingered on the pouch around his throat, seeking comfort in the familiar texture of the leather. This talisman had been with John for years. Touching it was calming. “You don’t own me, Sherlock.”

And John began to swim.

With determined strokes, John threaded his way through the accommodatingly mild waves and out into the open ocean, heading for the horizon. He needed to get far enough out to avoid the mysterious currents. The ocean was pleasant enough that morning, if chilly, and John strove to keep a sustainable pace. It would not do to exhaust his stamina prematurely.

Even the birds seemed happy that the weather had cleared up, and were flocking in noisy clouds. A cormorant landed on the water not far from John.

“Hello,” John told it, blowing out into the salt spray. “Come to keep me company, have you?”

The cormorant stared at John through one eye, picking at a bit of floating detritus. John felt the slow burn in his arms as he cut through the water with powerful long strokes. It probably wasn’t necessary to go this far out, but John knew that currents were dicey. He would rather go too far than not enough.

The cormorant, to John’s surprise, stayed with him.

After days with only unpredictable Sherlock as company, John felt warmly toward it. Something about the crazy look in the bird’s eye reminded John of Wylie Clegg, the old sailor who was so often into his cups back on board the HMS _Endymion_.

“You’d better lay off the grog, Wylie, or Emma will make good on her promise to go back to Glasgow,” John told it, spitting out a mouthful of sea foam.

The cormorant opened its wings slightly to adjust for a rocky wave and watched John as he changed course. The waves were accommodating, and the trip inland was much faster with the boon of the surf at his back. When the beach was in sight, John checked for signs of Sherlock, but his luck held and he made it into the shallows unmolested.

The sand felt like victory.

Whooping, John broke into a soggy jog, flinging his arms out and clicking his heels together in the air, jolly with his success. He turned around to do another giddy victory lap, but something crunched beneath his bare foot on the beach. He squatted and brushed away the sand to see what it could be and --

“TARNATION!” cried John, leaping back in the sand as if he had been burnt.

It was a human finger, rotted away to mostly leather and bone. John didn’t have much time to process this, because he caught a flash of darkness in his peripheral vision and reacted instinctively, rolling away from the waterline and clawing to his feet. Sherlock’s hand snatched closed on empty air where John’s foot had been. 

“ _John Watson,_ ” Sherlock’s voice was baritone thunder.

John scrambled for the sanctuary of the treeline where the sand turned into dirt and vegetation. He peered from behind a sagging palm at Sherlock, who had plowed out of the ocean and partially onto the beach, arm still outstretched.

John’s heart hammered in his breast. _He almost had me_.

“Sherlock!” John shouted back, fear making him furious. “What the bloody hell do you think you’re doing?”

Sherlock held his upper body up on his forearms, his heavy tail streaming back in the lapping ocean waves and anchoring him to the sea. The sand had churned up around the merman with the violence of his sudden emergence.

“Come back now, John,” Sherlock commanded, face whiter than usual with fury. “Come back now and I will not kill you.”

“Mm. Tempting,” replied John. He came out from behind the tree warily, a suspicion germinating in his mind.

Sherlock was staring at him, and actually seemed to be panting with panic. “John,” he said. “John, _come._ ”

And John realized: Sherlock couldn’t come any farther onto the island. He had done it. John had made it to the other side of the island, and now he was safe. Admittedly, the first thing he had found on the island was a human phalange, but even that couldn’t put a damper on John’s success. Sherlock’s expression soured further as he read the triumph on John’s face and in the straightening of his shoulders.

John grinned. “Sorry, I’m a bit hard of hearing. You’ll have to come closer if you want to talk. Like _a_ civilized person.”

Sherlock’s nostrils flared and his eyes narrowed into livid slits. But John’s confidence was as great as the stretch of land between them. He picked up a sturdy looking piece of driftwood, thinking it could be useful in the construction of some kind of shelter, and hefted it jauntily over one bronze shoulder as he strutted along the beach.

“John. Come back into the ocean!” demanded Sherlock. Anger turned his voice to molten metal.

John whistled under his breath and stopped to examine a shell. It was pretty. “Hmm. Nope.”

Sherlock’s hiss was audible.

“Is that as far inland as you can come?” John inquired mildly. “Really, it’s quite nice up here. I don’t mind at all if you want to join me.”

It was cruel, John knew, but Sherlock had been cruel to him first. Sherlock was clearly very reluctant to come on land. Looking at him, John understood why. Sherlock’s enormous tail, as beautiful as it was in the water, probably weighed too much to pull through the additional drag of the sand. Sherlock could easily exhaust himself within a short distance. If Sherlock rested his arms for too long on land, he might never find sufficient reserves of energy to make it back to the ocean.

Sherlock ignored John’s taunt and tried a different tactic. “The island is dangerous.”

“So are you. I’d rather take my chances with the island. Leave me alone, Sherlock.”

Sherlock drew upon his old standby: “You promised, John.”

But John was prepared for that. Without missing a beat, John replied, “Yes, I did promise to answer any questions you may have, and I can still do that from here. Ask a-bloody-way.”

The merman fell silent, tail slashing agitatedly. “Fine,” said Sherlock at last.

His voice had none of the hysteria of moments before; now, it was calm and almost meditative. John stopped where he was pretending to examine the bark of the palm tree, unnerved by the sudden change in tone. He turned to see Sherlock pushing himself back into the ocean. In that dreadfully calm voice, Sherlock said:

“You can’t stay on the island forever, John. Believe me. And when you try to leave, not if, but when, I will catch you, I will claim you, and I will _never_ let you leave my cave again, for all the rest of the days of your puny human life.”

A wave rolled up then, and Sherlock vanished into it like a magician’s trick, leaving John conspicuously alone.

~  ~

Now that he was unshackled from his merman captor, John’s survival was in his own hands. Proud of his restored self-reliance, John developed a loose plan, a charcoal sketch of survival in his own mind.

It took him only a couple hours to explore the island perimeter and might have taken less time if John had not been collecting anything that could potentially be of use. The island was forested, peppered with worn old palm trees near the beaches, and hardy scrub farther inland. Some of the plants looked sort of edible, but John was not stupid or desperate enough to test that.

He saw no immediate evidence of large animal life on the island. There were, however, an abundance of sea fowl and blue crabs crawling the beaches; a potential source of meat. John could see fish swimming in the shallows off the beach, too, but Sherlock’s presence was a constant threat. Just because John could not see Sherlock in the immediate vicinity did not mean that he could not erupt from the water like a realized nightmare, stealing John back to the grotto or eating him alive piece by piece. So, John stayed well clear of the ocean.

At one point, John was forced to stop and go back the way he had come, progress halted by a rocky butte too steep to climb. It was the back side of the rocky outcropping that contained Sherlock's grotto on the other side.

[ ](http://archiveofourown.org/works/1669427/chapters/5420015)

On the southeastern side of the island, John came upon a large bushy tree. It was like a fir but thorny and unlike to the other flora. It sat upon a sandy knoll sprinkled with grass near the beach. The green bristles of the tree were naturally bowed in, creating a scoop that John supposed he might be able to use as the foundation for a shelter. Best of all, the ugly tree was far enough inland that John was confident of Sherlock’s inability to reach him.

The sun was high in the sky by the time John began combing the beach to look for materials for his shelter. He found some more driftwood, water-damaged and warped by the sun. He braided some of the branches of the ugly tree together into a roof atop the natural gaps in the foliage, pruning away branches that did not serve his purpose. He packed the dry soil flat, and finished his effort by leaning the driftwood planks inward against the tree trunk to act as a wind barrier.

“Not terrible,” he told himself as he surveyed his work.

Under this crude shelter John deposited the things he had collected: three green coconuts, a sharp flat rock, a heavy branch that would serve as an improvised truncheon, and a giant green leaf with a fold in the middle that still held a quantity of rainwater. There was no place on the island proper that had natural temperature control like the inside of the sea cave, but John hoped the tree and driftwood would subvert the worst of the night winds. He wiped the sweat off his brow and turned to squint out at the sea, which was painted orange by the sunset.

John felt... good. Cautiously optimistic. In control, even, until he spotted saw a flash of white out on those calm evening waves, and then his optimism turned to ashes in his mouth.

Sherlock was out there, trawling the waters like a shark. Waiting.

~  ~

The first night on the island was hard.

The winds were worse than John had foreseen, and he dug into the ground like a burrowing crab, kicking sand and soil over himself just to have a barrier against the chill. He cursed Sherlock for stealing his trousers. His shirt-turned-kilt provided no warmth. He drifted, a bit, but then the sudden thought that Sherlock had somehow crawled all the way over the beach and up onto the knoll woke John; he snatched up his sharp rock and stared furiously out at the silver-lit beach.

There was no sign of the merman. 

John’s paranoia did not abate. It lingered in his bones like an infection that prevented rest. John was so uncomfortable, both physically and mentally, that he did not realize he had even succeeded in slumbering until the sunrise woke him.

Fortunately, daylight brought with it a renewed sense of pragmatism. Survival was John’s priority. He would be fine, Sherlock or no, as long as he did not succumb to panic. John opened one of his coconuts -- the first one turned out to be rotten, but the second was good -- and from that he hydrated himself and ate, and when he was done he kept the hollow shell for a bowl. This started a chain of industriousness that saw the shelter improved by digging a shallow pit in which he could lay, and rearranging the driftwood wind barriers. 

John caught a crab, hoping to eat something more substantial than coconuts. Unfortunately, the crab interior was naught but black goop. Disgusted, John threw the it out onto the beach. The cormorant landed nearby. John was fairly certain this was the same bird that had followed him on his swim.

“Hello there, Wylie. Come to visit me again?”

The cormorant cocked its head to the side at the sound of John’s voice. It quarked and eyed the crab.

“Oh. By all means.” John told it.

He gave the cormorant some space, and Wylie waddled over and began to peck at the crab.

“I can’t believe you actually want to eat that. Well. That’s another thing you have in common with the other Wylie, then. As I recall, he’d eat just about anything that didn’t run away from him... and some things that did, besides.”

As he spoke, John, strolled slowly along the line of scrubby vegetation in search of wood that had escaped saturation by the recent rains. He found some, and John scooped a shallow pit in the sand and crouched over it, wedging some fluff into a crack in a piece of dry wood. The next half hour was an exercise in frustration as John furiously rubbed the blunt end of a stick into the the groove, sweat trickling down the line of his spine and pooling in his lumbar area.

A tendril of smoke curled out --

before the wind snuffed it.

“The wind!” John cried in dismay to Wylie, who croaked nervously and shuffled away.

Growling, John hunched over the wood, redoubling his efforts and repeating the process until another thread of smoke rose, and this John cupped as tenderly as a lover’s face, breathing gently onto the newborn flame until it at last flickered to life and accepted his offering of kindling and dry wood. The fire grew, and John let out a great shout of triumph and looked around.

But there was no one. Even Wylie Clegg had lost interest and flown off.

That was fine, it just meant that no living soul was there to witness the manic, neanderthalic dance of triumph John indulged in around his newly-made fire. He. He John. He had created _fire_. He was the embodiment of human progress. John went back to the beach to look for crabs to cook, and that was when he aspirated his own spit in surprise. Sherlock was in the shallows, chin pillowed on his strong forearms as he gazed at John.

John froze. How long had Sherlock been observing him?

Sherlock smiled slowly, but did not otherwise move. The waves split and opened on either side of the merman’s slender torso, a gleaming envelope. Sherlock reached out his white hand to John in slow, silent invitation: _come to me_.

John swallowed around a hard lump in his throat.

He shook his head. _No_.

Sherlock’s smile faded.

The merman dropped his hand, and pushed back in the sand at exactly the moment the next wave rolled in; by the time the water pulled away he had vanished like a figment of John’s imagination.

~  ~

On the second night, the moon was bright and the beach illuminated in shades of monotone grey. John was awoken by a feeling of such despair that it seemed he might be crushed underneath the weight of it.

John curled his arms around himself and sobbed, rolling into a fetal position while tears burned wet tracks down his cheeks. It was as though every hurt and sorrow John had ever known was brought to the surface, fresh as a new wound. Disoriented, it took John some seconds to realize that the source of his misery was not the familiar poison of a nightmare at all, but provoked by something external:

Sherlock was _singing to him_.

The music did not sound like human singing at all, but somehow John knew that was what this was. Low sounds rumbled up the beach in pulses, filling the air with a throaty hum. It seemed like many voices were singing at all different pitches, with Sherlock’s distinct baritone rolling thunderously underneath it all. John knew, even before he spotted the lone figure in the moonlit waves below, that this was Sherlock’s doing. He recalled legends of sirens singing men to a watery death.

Apparently these legends held truth, for John felt compelled to the sea. He was on his feet and halfway down the grassy knoll before he realized what was happening, knowing that the balm for his aching soul was in the ocean - the music told him so. Sherlock would make it better, would ease his hurt. He had to hurry - wait, no. John was emotionally raw and confused, but there was one truth of which John was absolutely certain: he did not want to go back to Sherlock. Alarmed, John stumbled in the sand and fell to his knees with a gasp.

_What on earth..? Am I dreaming? Oh god, it hurts. Make it stop._

But then the music Sherlock was producing intensified, and John surged upright with the gracelessness of a drunkard, desperate for relief. He was bleeding out inside, bleeding out with sorrow, but it would all be all right, if only John could just make it into the water. To Sherlock. He was closer, now, and could see the merman out in the water, silhouetted against the white disc of the moon.

John was not the only one compelled by Sherlock’s siren song. Crabs emerged from their hidey-holes in the sand and made their way slowly to the sea, so many of them that the beach was covered in a carpet of tiny marching carapaces. Sherlock was a skilled fisherman, his music was the net, and every living creature on the island his catch - John included.

 _Come into the water, John_. _It doesn’t have to be like this_.   _I’ll make the pain go away. Let me soothe your hurts._

“No,” gasped John.

But the music droned on.

John was nearing the shoreline, now, and the sea spray on his face brought him back to himself.

_No. It’s Sherlock. He’s doing something to me - tricking me. It’s all in my mind!_

John’s foot caught on an exposed rock and he crashed onto his knees for the second time, catching himself on his hands with a dry sob of fury. _Damn you, Sherlock!_ John shook his head, clenching his fists in the sand until the grains dug into his palm. He saw a broken oyster shell and he snatched it up before his sound-drugged mind could distract from his intent.

John plunged the razor-sharp edge of the shell into his hand.

The pain was sharp and immediate.

John howled in agony, dropping the shell and staring at the blood that welled up and rapidly filled the trembling cup of his palm. The moment John slashed himself, Sherlock’s song began to fade, and with it the supernatural sorrow. Sherlock looked fascinated, cocking his head to the side and squinting at John as though he were trying to visualize the anatomy beneath his skin. He drew closer, tail lashing behind him in a swoop of silver above the waves.

John lifted his ruined hand to his face, and, still making hard eye contact with Sherlock, wiped red-black blood across his own face. It was defiance, loud and clear. _I am in control of this body. It is mine, to hurt and keep, to control and bleed, if I wish it._ John saw Sherlock’s breath hitch. John felt his own body heat in response, a convoluted and definitely sexual response that he was not anticipating. What was wrong with him?

“John…” Sherlock’s voice was a soft baritone rumble. His pale eyes gleamed in the moonlight, and his body leaned inland, toward John. He looked besotted.

“Leave me, Sherlock,” whispered John, throat hoarse.

Sherlock, for once, complied.

~  ~

_*The closest approximation to Sherlock’s siren song would be tuvan throat singing, albeit a deeply compelling, supernaturally velvety version._

 

**Notes for the Chapter:**

> The story is a bit more of a slow burn than I anticipated. It will be worth it. All the finished porn scenes on my harddrive says so. Did you know this fic started out as just a quick prompt fill? Goodness, look how it's ballooned up. This particular chapter was totally inspired by Tom Hanks in _Castaway_.
> 
> I will be out medieval camping next weekend (10/15 -10/19) and obviously won’t be able to write or post fanfic from the middle of the deep forest, so Riptide Lover will be updating late. Yes, I know I go camping a lot. It’s just so I can commune with the fey. I plan to be back to the usual update schedule after that! :) If you get antsy, check [my tumblr](http://jinglebell-fic.tumblr.com/) for RL news.


	6. Undine

**Summary for the Chapter:**

> In which the boys come to a better understanding of each other. ~makes kissy noises~

**Notes for the Chapter:**

> I'm back, did ya miss me? For those of you who missed it, there's now a [map of the island](http://archiveofourown.org/works/1669427/chapters/5420015) embedded in Chapter 5. As an aside, my beta readers JP and Dee are enormously talented humans. Also, Dee is an artist, go check out sier [blog](http://otterystmarymorstan.tumblr.com/tagged/my-fanart)!

Sherlock left John well alone for almost a week after the Singing attempt, although he periodically made his presence known. John became accustomed to seeing the glitter of sunlight on dark scales off shore. During that time, John tended to the wound on his hand, improved his shelter, and industriously prepared for long term survival.

By now John’s beard had grown in handsomely, several shades darker than the hair on his head, and he finger-combed it to the best semblance of tameness one could expect. Whiskers weren’t the only new addition to John’s primitive lifestyle. He learned how to catch, and bake, crabs. John ate a lot of crab. Most of his days were spent fashioning tools; John used a sharp piece of rock to shave branches into wicked natural javelins. He hoped that there would come an opportunity to hunt the fish in the shallows, despite the omnipresent threat of recapture. When his energy was low, John discovered how to sit quietly and weave strips of bark into crude rope. 

Wylie Clegg liked to grace John with its presence. The cormorant would sometimes bring its catch onto the beach for consumption, far enough to discourage John from trying to take its haul, but close enough that John could watch as it gluttonously swallowed down fish that seemed far too large for it.

“You trying to show me how it’s done?” John asked, smiling good-naturedly as he deftly twisted the end of his latest rope to finish it. The bird cocked its head and stared at John through one yellow eye. Then it flew off. John drew the rope across his palm unthinkingly, and was rewarded for his negligence with a shock of pain. "Blazes."

Back on board the _HMS Endymion_ , John had been close with the ship doctor. Intimately close, in fact. John flushed at the memory of Sebastian’s cockstand sliding hotly against his while they panted into each others mouths in the doctor’s quarters, cramped, and freezing in terror of discovery at every subtle creak and groan. If Sebastian were with him now, John would be told off for failing to care for his wound, allowing it to develop a yellow crust.

John folded his fingers down carefully over the cut on his palm. His idle thoughts turned to Sherlock, that damned siren.

Sherlock.

John was familiar with the myth of the mermaid. It was a popular tale amongst the navvies. Singing a sailor to his death seemed to be one facet of the legend that held truth. John wondered how many men had actually survived an encounter with a merman, or mermaid. If he ever made it back to London, John wasn’t entirely sure he would want to relate his adventure -- who would believe him? And if they did, it could only mean trouble for Sherlock. Sherlock was fierce and bright and intelligent beyond all reckoning.

John sort of wanted to be near him.

There was a thrill to being in Sherlock’s presence that John found difficult to articulate. John knew himself well enough by now to be aware that his attraction to risky situations was pathological. Despite the fact that Sherlock had nearly drowned him, not just once but twice, had brought John to gasping climax without so much as a by-your-leave, and compelled him with his siren call, John found himself more bemused than properly furious. 

Sherlock did not seem to know better. Perhaps, with a patient enough tutor, Sherlock could become civilized company. Now that John was no longer confined to the grotto, perhaps they could continue their conversation and come to mutual enjoyment.

John went and stood near the shoreline. “SHERLOCK!”

His shout seemed to be swallowed by the waves.

John tried again. “OI! SHERLOCK.”

“No need to shout.”

John looked down the beach, where Sherlock had emerged from the waves as silent as an owl’s wing. His black curls glistened. John didn’t know how the merman always seemed to be within easy swimming distance.

“Hello,” John said.

The beginnings of a sneer wrinkled Sherlock's nose. “You called for me.”

“Yes. I… I thought we could talk more. I could answer more of your questions.”

Sherlock’s eyes narrowed. “Why?”

“You’re curious, and I made a promise,” John said. Then, feeling exceptionally honest, “I want to know more about you, and your people. I think we could be friends --" he stumbled over the word only a little. "Start again, perhaps?”

Sherlock laughed, and the sound was like rolling on shards of glass. “I tried to drown you. I Sang you to me, John, and you preferred to stab yourself to avoid mine own embrace.”

John’s wounded hand throbbed when it was mentioned. “Yes, well, maybe if you just asked me instead of doing what you pleased without warning --”

“Will you come into the water, John?”

“No.”

“What is the point of asking if it does not work?” snapped Sherlock. His tail snapped in the waves agitatedly and sent a colossal wave rolling back out to sea. Alarmed, John held up his hands in a placating gesture. He saw the moment Sherlock’s eyes focused on his cut palm. John strove to keep the movement natural when he self-consciously dropped his hand back to his side.

“Why did you resist mine own call?” Sherlock murmured, strop circumvented by the distraction. He sounded petulant.

“You liked it,” John threw the merman’s words back in his face with a deadpan expression, causing Sherlock to jolt. “If you always got what you wanted life would be boring, wouldn’t it? You're so terribly bored, living out here all alone. Aren't you.”

Sherlock’s pupils dilated. He drew closer inland, and John assessed the distance between them and stepped back. Sherlock whined in the back of his throat, soft and manipulative and just a touch unearthly.

“No,” John said firmly. He suppressed a shiver. “None of that. Unless you promise you won’t steal me back to that damned cave, I’ll thank you to keep your distance.”

The merman slouched forward in the water until he was lying on his belly on the sand while the tide glided back and forth over the wet muscles of his back. “I won’t promise that, John.”

John did not feel like starting an argument, he was too starved for company that could actually speak back. He sat down in the sand a goodly distance from the merman and segued into asking the questions that had been niggling at his mind for the past week. Sherlock would stay, or Sherlock would leave. "What does your kind of people? Of humans, I mean."

Sherlock propped his chin in his palms. “Mine own kind prefer to keep their distance. Humans are dangerous on board their own ships -- most prefer to Sing them to the sea. Then eat them.”

John took a deep breath and steeled himself. “Why do you eat humans?”

“They taste good.”

John spluttered in horror, but then he saw that Sherlock was smirking a little bit and John's spluttering turned into a constricted chuckle. Damn his gallows humor. “They do _not_ , Sherlock. Heavens!”

“So you have eaten another human before?” Sherlock inquired, curious and non-judgmental.

“What? No. No!”

“How can you be certain, then, that a human does not taste good?” Sherlock’s grin exposed his pointed teeth. He was ribbing now.

John needed to steer the conversation to less treacherous waters. The subject of people-eating was a battle John was not going to win today. “Not going there, Sherlock. What do _you_ think of humans?”

Sherlock gave John a calculating, rapid assessment. He hadn’t been expecting that. John trusted his gut feelings, in all things, and his gut was telling him that Sherlock -- despite being John’s only example of a merman -- was atypical among his kind. He had couched his questions deliberately in order to suss out just how far removed from merfolk society Sherlock considered himself.

“I have not interacted with many humans. And… rarely under circumstances that facilitated dialogue,” Sherlock finally said. A non-answer.

“I haven’t interacted with many mermen, either,” said John.

Sherlock’s eyes glittered with amusement. “I should think not. And what of you, John Watson?”

“What of me?”

“What do you think of us?” John wasn’t born yesterday. Sherlock might have said _us_ , but what he meant was _me_.

John replied honestly, “You fascinate me.”

Sherlock shook a wet curl over the delicate fan of his aural fin. “Go on.”

John’s smiled. _Goodness, he’s just free in his vanity, isn’t he?_ Luckily for Sherlock, John was not the sort of bloke who was stingy with his compliments. “You’re quick. You can speak English, somehow, and your accent is upper-class, so frankly I don’t believe that you learned English by listening to sailors on the docks. Not exclusively.”

“Clever.”

Encouraged, John continued: “You’re different from others of your kind, I think. I don’t have a basis for comparison, I realize, but your mind is -- it’s…”

John must have been searching for the word, or the courage to say it, for too long, because Sherlock drew closer.

“It’s..?” he prompted, and in that moment a crystal bead of water fell from his glossy black curls, traced a stripe down the column of Sherlock’s neck, and came to a quivering rest at the base of his neck. 

“Beautiful,” whispered John, watching the water drop tremble in the divot of Sherlock's suprasternal notch.

Sherlock lifted his caudal fins out of the ocean behind him and flared them out abruptly in a giant white peacock fan. John was suddenly furious that no one was there to bear witness to this but him, for the imagery was so striking that John felt very strongly there ought to be a painting of that made. And since he was clearly being invited to look, John did so unashamedly. Sherlock drank in John’s reaction with that little crooked smirk, incongruously playful, on his aristocratic features.

“Filled with humility you are,” murmured John. Sherlock smiled and let his fins slide back under the waves. John realized that he had become relaxed in the course of their conversation, lulled into a sense of security. Of course, as soon as John became aware of this, he tensed up again. Sherlock’s brow pleated.

“What is it?” he demanded.

John wasn’t sure what it was. He felt a worm of anxiety at the unidentified feeling he was experiencing. He stood and brushed the sand off of the back of his thighs. Clearing his throat, John glanced back at the ugly tree on the knoll. His new home, for God knew how long.

“I should… I have things to do, now,” John meant to terminate the conversation there, but he heard himself say aloud: “Why don’t you come back tomorrow?”

Sherlock frowned at him, clearly a bit put off.

“Or not,” John said lightly. “It’s all the same to me.” _It really isn’t. You’re the only stimulation I have, here. I think I’m going a bit mad._

He hurried back up the sandy slope, filled with a resentment and frustration he could not name. He did not look back.

~  ~

It turned out that Sherlock did return the next day. And this time, he bore a gift; an enormous yellowfin. John’s mouth watered and Sherlock pitched it to him (John grunted when it slapped into his arms, cor the thing had to weigh almost thirty pounds) before he’d even made it down to the shoreline. John immediately turned right back around in order to hoard the fish in the shade of the ugly tree, and he shook sea water from his fingers when he came back down to the shoreline. 

“Ta,” said John, and meant it. “That is going to be delicious.”

The merman did not acknowledge the gift at all. By way of greeting, Sherlock said, “I want to touch you.”

Memories of awkward pleasure spent gasping in the steel coil of Sherlock’s arms surged through John. His face heated. Just what kind of touch was the barmy creature thinking of? “I don’t know about that,” John said. “I don’t trust you not to steal me away again.”

Sherlock had thought of this. “For today, I promise not to steal you away. Unless you ask me to do so.”

 _Like I’d ever ask you to take me back to your lair._ Sherlock looked neutral, sincere - but John was not convinced.

“Hmm. No. Say! there’s something I’ve been wondering, Sherlock.”

Sherlock’s pout at being denied transformed into reluctant interest. “Ask.”

“Who makes the rules? I mean, amongst your people -- do you have a king? Do you have a city?” Visions of vast underwater palaces and undiscovered aquatic shrines crusted with the treasures of a thousand shipwrecks manifested in John’s mind. But Sherlock was already shaking his head.

“Mine own people do not have rulers. Our females are nomadic and the males solitary,” A pause. “What is a king to you?”

“A king -- a king is a supreme ruler, over the other people. He makes decisions and guides progress, see. We have a Queen -- that’s, er, a woman king -- right now. Her Royal Majesty, Queen Victoria.”

The current Prime Minister was Lord John Russel, too, although John wasn’t sure if he was prepared to explain current politics to a merman.

“We have no formally recognized king,” Sherlock said slowly, stroking his clawed fingertip over the succulent curve of his own lower lip. “Although there is one who refuses to give up on trying to unify us.”

“Oh?”

“Yes. Mine own clutchmate, Mycroft.”

“Clutchma- oh, er, right.” _Not human. Right. Right then._

Sherlock smirked at John's discomfort. “Mine own brother, if you prefer. Mycroft is his name.”

“Oh! Mycroft is a person!” cried John, sitting down in the sand. Sherlock’s eyebrows contracted in puzzlement. 

“The other day, you said ‘Mycroft’ and swam off. I had no idea what you were talking about.”

“Ah. Yes, he had entered mine own territory again. He thinks he can stick his big nose wherever he likes without consequence; I had to go chase him off,” Sherlock's voice was crisp with irritation. John shifted uncomfortably, and Sherlock saw the motion. His eyes softened. His tone of voice turned wheedling and persuasive. “I won’t steal you away this day. Let me touch you -- just your face this time, nowhere else.”

Oh, heavens. That baritone register might as well have been a soft tongue on John’s inner thigh. Sherlock capitalized mercilessly on John’s hesitation. “You may touch mine own body, also, John Watson... fair is fair. You find me beautiful,” Sherlock added smugly, and turned to display his humanlike assets to best advantage. 

“Promise you will not steal me away to the grotto, or try to drown me,” John said sternly.

“I promise not to steal you away to mine own nest, or drown you on this day.”

So John waded down into the water and leaned over. Sherlock rose into a sitting position by curling his huge tail beneath himself that they were of an almost equal height, although John still had to tip his face up to look into the merman’s eyes. Sherlock’s body was that of a beautifully-proportioned man, except where it wasn’t.

“This is new,” Sherlock remarked, gently carding his fingertips through John’s honey-colored whiskers. His touch was so gentle that John’s breath caught in his throat. This close, John could smell Sherlock, and the odor was not fishy at all. He smelled of salt, yes, but no more than any human who had gone for a swim -- and under that John detected ozone like an unrealized thunderstorm. Underneath all of that was the faintest hint of marine creature, the spice of ambergris.

Then Sherlock leaned down and stroked his lips slowly and tenderly over John’s beard. John stiffened as his body immediately interpreted the action as a kiss, although his logical mind knew that Sherlock was merely cataloguing the texture of his whiskers. After a moment, Sherlock was satisfied to draw back and stare at John from under a lace of black lashes.

John studied him in return, finding that Sherlock’s face was more familiar to him now. If this was another man, John never would have been so forward, but since it was just the sky, the ocean, and Sherlock, John found himself stroking Sherlock's pronounced cheekbone with the callused pad of his thumb, feeling the glittering bumps of tiny scales there. Sherlock gazed down at him serenely. Only the flex of gills at the hinge of his jaw belied any interest in the proceedings.

 _This is dangerous. You should get out now while you still can_ , whispered the little voice in John’s head. John ignored it. Sherlock leaned forward, such a microscopic motion that John only detected it on a cellular level but he found himself responding in kind, cool breath on his mouth, and John waited and waited but Sherlock did not move to breach the distance, that hateful sliver of space. 

So John kissed Sherlock.

This surprised them both. Sherlock’s lips were cool and soft but firm at once, and he yielded to John and sunk down slightly to grant better access which John took advantage of, carding his hands into Sherlock’s curls possessively to hold him in place. Sherlock made a soft sound deep in his throat in that supernatural way of his, without interrupting the slick slide of lips. He took John’s hips in his hands.

John stood knee-deep in the sea, unable to oppress his needy mouth, his covetous hands, his heart beating out the mortifying truth. He desired Sherlock, as a man desires a woman or, in John’s case, another man. He broke for air. Urgently, John’s mouth roved across the merman’s face, peppering his porcelain cheeks with bristly kisses. Sherlock was unexpectedly docile in the face of John’s passion, parting his lips in invitation when John returned to them.

John was beguiled by Sherlock’s receptiveness to his advances; he coaxed him onto the damp sand just out of the water and straddled the solid length of Sherlock’s tail, mounting him. If the croon of pleasure was any indication, Sherlock liked having John in his lap. He pet his hands down John’s naked body, grabbing greedy handfuls and squeezing just shy of too firmly, a hint of the devastating supernatural strength dormant in his elegant fingers.

John’s blood roared over reason. He felt strong and powerful, his cock hard and spearing into the fabric of his kilt. He suckled a love bite into the salty column of Sherlock’s throat. He could feel Sherlock’s pulse throbbing excitedly in his neck. John deliberately brushed his whiskers over that tender skin on his way back to Sherlock’s mouth.  John caged Sherlock's face in his palms. He felt the flutter of gills against the heel of his hand and couldn't help but smile. _As if I could forget who I was kissing._ He leaned forward and planted a final, chaste kiss on Sherlock's lips and drew back to gaze into those seaglass eyes. Sherlock's pupils were as close to roundly human as they ever came.

“Have you put some kind of spell on me?” John huffed, only half-teasing.

“No,” whispered Sherlock. His breath was shallow.

“Then what have you done to me?” John said hoarsely, his cockstand throbbing where it was cradled in the hollow of Sherlock’s abdominal muscles.

Sherlock just smiled. The tide lapped at the braid of legs and tail. John had fallen upon Sherlock, who held him up so effortlessly that it took him a moment to realize Sherlock was using his core strength alone to support their combined weight, as his hands were occupied with tracing slow patterns across John’s back.

“Amazing,” whispered John.

Sherlock inhaled sharply and leaned his face down to stroke his lips over John’s beard again, gliding upwards to nuzzle into John’s sandy hair. It was a rather intimate gesture, the sort of thing one might do with a lover after pleasure, and John’s cock throbbed. He ground his erection firmly against Sherlock. It wasn’t as though Sherlock weren’t already familiar with that part of his anatomy, after all. But as John stroked against wet scales once more, the merman beneath him suddenly went stiff as a plank and made a surprised little noise that was so blatantly sexual that John whirled on Sherlock and bit him gently on the throat, then sucked a new mark there. Sherlock made that noise again and John felt spurred to an almost heady state of lust. Something caught John’s eye and he paused. There was a slit between Sherlock's pelvic fins, shell-pink and as inviting as a vulva. John was absolutely certain that had not been there before. He scooted down Sherlock’s tail in order to see better. John's hand ghosted toward it and was halted by the sudden press of strong pelvic fins clapped on either side of his wrist.

Sherlock was eyeing him carefully.

“Ah. Sorry, that was rude, I –- I wasn't thinking.”

John didn't know why he was apologizing, considering that Sherlock had touched John's genitals so soon after they had met. But Sherlock dipped his chin.

“It's natural to be curious,” he remarked at last, and his pelvic fins released John warily.

Well. John decided to take that as invitation. He let his palm hover over the slit in Sherlock's groin; it felt warm under the water and was slightly swollen. Oh, this was awkward. Did –- did mermen have fish anatomy, down there? How did they copulate? Where was Sherlock’s cock? Was Sherlock a _woman_? John's confusion must have been broadcast on his face, because a baritone chuckle startled him into looking back at Sherlock's face.

“I am not a female, if that is what you're wondering. The females of my kind travel only in the deep ocean, in sorority pods. They come inland once a year to seek a mate. We – male undine, that is --”

“Undine?” John interjected, grateful that Sherlock wasn’t going to leave him floundering in confusion.

Sherlock waved dismissively. “It is the word for mine own people. As your own kind call yourselves 'human', we call ourselves undine.”

 _Apparently merfolk is the wrong term_ , thought John. He gently pressed his palm against the slit, and a surge of desire filled him at the plump slick heat. Sherlock’s abdominal muscles contracted. Sherlock's voice, when it came, was tremulous. “M-Male undine live in shallower waters, as a general rule. Your species does not display the sexual d-dimorphism of mine own.”

“What are the females like?” asked John, curious. Visions of beautiful sirens filled his head. If Sherlock was indicative of a typical merman, John figured the womenfolk must be almost too lovely to look upon.

“Frightful,” Sherlock replied honestly. “To you, they would seem as monsters.”

John swallowed around a sudden dryness in his throat.

“We do not mingle with the females unless it is the season for reproduction, which is known colloquially as the Riptide,” Sherlock paused, gills fluttering. “It's considered a bit of a vulgar term, actually.”

He looked slyly at John. John's hand was still on Sherlock's genital slit, and that felt rude somehow while they were having a discourse, so he removed it. The temperature of their lust cooled somewhat, usurped by their mutual intellectual curiosity.

“So, the women of your kind, they... travel out on the open sea?”

“All year round, with the exception of the Riptide,” confirmed Sherlock.

“Why do the men -- er, males, live closer to land? Is that how you found me?”

Sherlock lay back on the sand. He surveyed John through half-mast eyes, voice chocolatey with pleasure. “We are much smaller and weaker than our own females, John. We are... ill-equipped for the rigors of a nomadic sea lifestyle, so we build nests in our own territories and wait for the females to come to us.”

“During the Riptide,” John repeated, to confirm.

“Yes," Sherlock was amused at John using undine slang.

John felt his face heat with a realization. “Is the grotto..?”

Sherlock's gills fluttered slightly, which John had come to hypothesize was the undine equivalent of a blush. “Yes, these waters are mine own territory, and the cave is mine own nest.”

Another conversational trap lay that way. John reached for a safer topic. "So, the women. Do your... does your kind have live babies, like mine?”

Sherlock smiled. He undulated his hips up until they pressed delicately against the weight of John's bollocks through the material of his threadbare shirt. “My, my. Asking so many questions about reproduction, John. One might think you were getting ideas.”

John leaned in and pinched the fullness of Sherlock’s lower lip carefully between his teeth, and Sherlock looped his arms around John’s shoulders. He could feel the heat emanating from Sherlock’s inguinal slit through the fabric.

“Maybe I am,” John growled, soothing the gentle bite with a swipe of his tongue. Sherlock seemed content to let John kiss him as long as he wanted. When at last John drew back, they were both panting.

Sherlock cleared his throat and murmured, “I should like to see what you look like in coitus, John. Shall I find another human and spirit her away as well, bring her to mine own nest for you? Would you like that? I could keep her here, your own pet. You could mate with her anytime you wanted, and I could watch you... observe how your own kind copulates.”

John reeled back. “Sherlock! That is not on!”

Sherlock regarded him lazily. “Is it not?”

“No! Sweet Mary,” John scrubbed a wet hand over his face, erection flagging at Sherlock's casual mention of abducting a woman.

Sherlock made it worse by continuing to talk. “Oh. Oh. Or is that you are an invert, John? Do you prefer the masculine touch?”

“We’re done here,” John said shortly, removing his arms from where they had been looped under Sherlock’s shoulders. Hearing Sherlock’s words was taking John further and further out of the hazy pleasurable moment. Suddenly he wanted nothing more than to curl up under the ugly tree and eat his fish. Away from Sherlock.

“Why not, John?” rumbled Sherlock. His voice was cold silk on overheated skin.

John ignored him and dismounted, wincing as the blood rushed back to his feet. Sherlock was as unyielding as any ocean rock, but John was too proud to reach out and steady himself on the merman - not after what Sherlock had just said. He started to move toward the beach, and he saw Sherlock reach out for him.

“No,” John said sharply, and to his surprise the undine did halt. He drew upon his trump card to reassert boundaries. “You may have given me permission to touch you anywhere, but remember that you promised to only touch my face.”

Sherlock blanched. John realized that he was afraid, and that was intriguing. “Look, Sherlock. I was the one who solicited you,” John cleared his throat and it came out in a short bark of noise. “Was all over you, in fact. It would have been impossible not to touch me. So I don’t consider that breaking your promise.”

The release of tension was visible in the set of Sherlock’s shoulders.

John nodded. He made his way back onto the sand, as dignified as he could possibly be with his cock still at half-mast in his kilt, and turned to look at Sherlock, who was sitting stiff-backed in the sea with a stony expression. John squeezed water from his kilt and asked: “Why are you so keen on promises, anyway?”

Sherlock did not reply, and John’s curiosity only grew. “Tell me why. You’ve been trying to extract promises from me from the moment we met. In my world, promises -- well, they mean something, yes, but your regard for them is stronger than that of any man I have ever known.”

Sherlock shook his head. “You are correct.”

John had a sinking feeling that the undine was not referring to his remark on the significance of promises in merfolk culture. This feeling was proven apt when Sherlock continued, “We are done here.”

And then Sherlock slid into the waves like a panther melting into shadow. John threw up his hands in mute exasperation. Apparently, they had both touched nerves with each other during the course of their interaction. Perhaps we should just stick to kissing, thought John - and then, being a pragmatic sort of fellow, recalled he had an entire yellowfin to eat.

**Notes for the Chapter:**

> The year is 1866. I've been dropping hints as to where and when Riptide Lover takes place, but it's primarily a Man versus Nature and Man versus Himself tale. The island setting is as much of a character to me as John and Sherlock are! Also bear with the slow burn here, I'm trying to build something up. ~boogie~


	7. The Bargain

**Summary for the Chapter:**

> Thanks to redscudery and JP for beta'ing this chapter for me on short notice, you spoil me rotten and I appreciate you.

The next day, Sherlock did not return. John realized he could torment himself wondering whether Sherlock was going to return, dooming John to a lifetime of boredom and sexual frustration alone on the island, or he could use this time to go about his business as usual. He chose the latter.

It just so happened that John was investigating the southwestern side of the island for resources when a movement in the shallows caught his eye. John stopped chipping away at a crab hidey-hole and squinted at the shoreline. He always kept about twenty paces away from the sea, which he figured would give him enough of a head start should Sherlock come barreling inland after him. The water rippled and a merman emerged, stately and upright like the coming of Poseidon himself.

The new merman's voice was crisp and upper-crust. “Ah. I thought he might have found himself a new toy. He usually isn't so attached to his own territory.”

“You must be Mycroft,” John said warily, straightening up to his full height and doing his best to look inedible.

“Charmed,” replied the merman with the slightest dip of his chin. He sounded bored.

Mycroft looked quite different from Sherlock, and John drank in the sight with the fevered interest of an avid collector upon discovering a new specimen. The parts of Mycroft that were humanlike would pass as normal in London without a second glance. Mycroft's visage, rather unremarkable but for a spectacularly beaky nose, was dusted with a spray of copper scales in the same places Sherlock had them: cheekbones, forehead, and chin.

He was possessed of a royal bearing, with a proud set to his shoulders. Mycroft’s torso was softer - not thick with muscle like John’s, or whipcord-wiry like Sherlock -- but capable of working in powerful synchronicity with his tail. And here was where Mycroft’s genetics deigned to compensate for their indolence, for there was no way to describe that particular part of Mycroft’s anatomy as anything but regal.

Mycroft’s tail was, at its most basic, the same as Sherlock’s. He had two pelvic fins, a dorsal fin, and the terminating caudal fins. But where Sherlock was a dramatic black-and-white, Mycroft’s scales were muted oxblood with eggshell-colored stripes, ornate spines fanning out in fingerlike protrusions that together composed each individual fin.*

To John's eye, there was one key difference between the two undine. Mycroft was missing an adipose fin entirely. There was a ragged scar where this fin should have been, on the dorsal side of the tail several handspans from the end.  _I suppose even fearsome creatures such as these merfolk are subject to the dangers of the ocean,_ thought John.

Mycroft was examining John just as thoroughly as he himself was being examined. John wondered what he looked like to him.

He knew that the sun had baked him brown as a nut, and the weight he had lost in the weeks following the accident only made his musculature stand out in harsher delineation. To the Victorian ideal of masculine beauty, John would seem an unsubtle caricature. Funnily, back in London, Sherlock would have been considered quite fetching -- if he had legs, anyway. John’s only garb was the shirt- _cum_ -kilt, and the leather pouch on its thong around his neck. The only thing on his torso was a length of bark rope looped over one shoulder. John felt the sea breeze tickle his short, thick golden-brown beard. _Probably thinks me some beastly wild thing_ , John thought. 

They regarded each other in curious silence. John broke it first. “You're Sherlock's brother.”

Mycroft inclined his head slightly. “And you are human, and alive. The latter is an unusual trait for one in mine own brother's tender care.”

John didn't know what to say to that.

“I wonder,” continued Mycroft, “where you and mine own brother became acquainted?”

“Became acquainted!” barked John, shaking his head in amazement. After all he had been through! Referring to the circumstances in which he met Sherlock as 'becoming acquainted' was such an understatement that John couldn't help but laugh. “A storm cast me from my ship. The ocean took me,” John, superstitious, here grasped the talisman about his neck for fortitude, “and I thought it was my fate to drown. Sherlock came upon me then.”

“And he did not try to finish what the sea started?”

“He tried,” John said mildly. He recalled the alarmed look on the merman's face when John had snatched Sherlock bodily to him and demanded a breath of life.

Mycroft was staring at John with parted lips and squinted eyes, as though he could not possibly fathom what was provoking the sailor's smile. “How did you survive?”

“Sherlock breathed for me.”

Here, Mycroft's neck gills flared out in surprise and he sat back, sinking slightly in the water where he had propped himself on the great coil of his tail. “He _breathed_ for you,” echoed Mycroft, as though John had cast aspersions on Queen Victoria.

“I didn't give him much choice in the matter,” John clarified.

Mycroft's eyebrows flew into his hairline. “There are few who can make Sherlock do anything he does not wish to do.”

“Yes, well. I was going to die,” John muttered. To his surprise, Mycroft smiled, a tiny and conservative and real expression, and the sight of it made John relax the set of his own shoulders. “I'm John, by the way. John Watson.”

“Hello, John.”

“You've come to see why Sherlock has been missing, then?” John continued, keeping his wary distance despite the fact he had to raise his voice to be heard.

“Yes. You can come closer if you wish: I promise I will not harm you this day,” Mycroft said, the small smile still present on his face.

John immediately relaxed and strode down the beach, stopping at the waterline. At this distance, he could see that Mycroft’s splendid dorsal fins were possessed of three barbed spines. John would bet a groat they were venomous.

Mycroft looked pleased at his approach. “I see you've worked out how to negotiate with mine own people.”

“I have a question about that, actually," John said. He put his hands on his hips. “Why are promises so significant to your kind? It's the only way I know to prevent Sherlock from stealing me back to his grotto.”

Mycroft's eyebrows had resumed a more natural position on his face during the course of their conversation, but upon hearing this, they once again ascended. “Stealing you _back_? I assumed that Sherlock put you upon this island deliberately.”

“No. He took me to his nest, first, and when he left me alone I escaped and came here of my own volition.”

“You escaped?”

“Yes. Humans can swim, you know.”

“I know,” replied Mycroft archly. “What truly baffles me is that you managed to evade the guardian currents.”

“Is that what they're called? Pah! I've never seen wave formations like that before, and I've been on the sea for nineteen years.”

“You likely will never see them again,” Mycroft said primly. He assessed John with a piercing expression quite reminiscent of Sherlock. Mycroft seemed to come to a decision, and he said, “To answer your query -- mine own people must keep the promises we make. It is part of our... hmm, how would you say it. Our contract to the sea. To break a promise is to invite our own ruin, and to lose the ability to Sing or weave waves.”

John's hands fell to his sides. Was Mycroft saying what John thought he was? “The Singing I am familiar with. But to weave waves?”

Mycroft's eyes were muted blue. As John watched, the undine’s pupils contracted slowly into a cuttlefish squiggle and John experienced a sudden and conflicting urge to run and to stand his ground at the same time -- a response conditioned by familiarity with Sherlock’s feral episodes. Mycroft swept his hand in an arc away from his body, and  a great column of water erupted skyward behind him. The spray was so sudden that it startled a sea bird flying overhead. 

“Great Scott!”

Mycroft dropped his webbed hand. “Quite,” he agreed mildly, amusement showing in the faint crinkle of his eyes as John stepped gingerly away from the waterline.

“So those waves, near the grotto. Those are Sherlock's doing?”

Mycroft pursed his lips. He hummed. Was that an answer? Was it just a vocalization? The regal undine didn’t seem particularly inclined to elaborate further.

“Right,” John said after the pause stretched too long for him. “So if, if the undine break a promise, they lose their ability to make music and, er...”

“Wave weave,” supplied Mycroft patiently. He sank in the water in order to submerge his rib gills; John could see them flexing gently open and closed. “I must say, John, I am beginning to see why mine own brother keeps you. You convinced him to share breath with you, you escaped his cave, and it is taken in evidence that you are are capable of surviving with minimal assistance.”

John wasn't sure what possessed him to say what he did next, but say it he did. “I could use assistance. I must escape this island, Mycroft. Won’t you help me?”

Sherlock’s brother blinked his transparent inner eyelids rapidly. It was tricky to read merfolk, as they emoted reservedly by human standards, but to John’s eye it seemed that he had caught Mycroft off guard. He might have responded to John, but then everything happened at once and it was all John could do to keep track of events. John had a split second to perceive a flash of white in the waves before Mycroft took the brunt of an explosive splash caused by Sherlock, breaching. John skidded back inland to avoid the colossal wave that rolled up the beach, shoveling tiny crabs and debris before it.

“ _Mycroft_ ,” hissed Sherlock. His tail slashed furiously through the foaming water. He was in full threat display, neck gills flared out like fine lace on either side of his throat, caudal fins a stiff and trembling fan. His wicked claws flexed as though he would prefer them wrapped around his brother's neck. “Get away from him.”

Mycroft raised his webbed hands in a placating gesture. His own fins had initially flexed open in alarm, but John could see the moment Mycroft deliberately relaxed them and presented as unthreatening. His body language broadcast that there was no challenge here, no need to be upset.

“I was simply curious, brother mine. I have not seen you in the open water in some time. I suspected you might have found a new source of entertainment,” Mycroft's voice sounded like two different people speaking at once; an overtone hum that made John's wounded palm ache. “I see mine own suspicions were not unfounded.”

Sherlock snorted. “Very well: I have a human. You know now. Remove your great beak from matters that do not concern you.”

Goose pimples sprang up on John's forearms, but Mycroft continued speaking as though nothing were amiss at all. “He is not an uncomely specimen. And he is intelligent... for a human.”

It was John's turn to snort, as he rather disliked being spoken of as though he was not present. Both undine ignored him.

“I found him, fair and square. Go, Mycroft. Don't you have conference to take with your bird spies?” but the bite had vanished from Sherlock’s voice, and his fins were quieting.

“I take my leave. John,” Mycroft dipped his chin to John (who was so far up the beach by now that he was practically in the treeline). John nodded carefully back. He had a gut feeling that Mycroft would be more willing to listen to reason than his brother -- for John was beginning to entertain the suspicion that Sherlock’s obsession with him went even deeper than it initially appeared. He willed Mycroft not to forget his request for help.

 _Please_ , John thought, squinting across the blinding white sands at the vibrantly-striped undine. Mycroft tilted his head slightly to the side, and John knew that the unspoken message had been perceived. Sherlock monitored their exchange suspiciously until Mycroft disappeared into the waves.

Sherlock followed him, presumably to be certain that he was actually leaving. John thought he should return to the shelter of the ugly tree. Instead, he found himself standing in place and reflecting on what had just transpired. Why on earth had he asked Sherlock's brother for assistance in leaving the island? He had just met the second undine. He must truly be desperate.

Sherlock's sleek head popped out of the water and truncated John’s reverie before it could properly begin. He regarded John from beneath dark wet curls. John looked back. It was clear that they both had words to exchange, and John realized that the onus was on him to approach, for Sherlock could not come far onto land. 

“Promise --” John began.

“I promise not to kill you, or bring you back to mine own nest this day,” Sherlock recited quickly. 

John picked his way down to the shoreline. The sun was high in the sky and gleamed off of Sherlock's cannon-black tail. His body language was all snaky seduction now, trying to make himself look meek, and his expression was one of such unadulterated longing that John felt an answering surge of emotion rise up.

“Are you casting some spell on me?” John husked. He checked his desire to palm Sherlock’s narrow waist.

Sherlock shook his head coyly.

“I think you are,” breathed John. John figured he must be a little mad for lust and emotion to surge within him from mere proximity to Sherlock.

He did not enter the water.

“What did Mycroft tell you?” Sherlock wanted to know.

“He told me about the nature of promises.”

Sherlock scowled. “Did he.”

“Yes. Sherlock, I must get off this island.”

Sherlock's voice was velvet over steel. “No. You already have plenty of freedom to do as you will, and you do not need a larger territory than this.”

“I don't care about territory. I miss other humans. I miss --” _London_. John's throat tightened.

“I offered to bring you another human,” Sherlock pointed out.

“That is not the same thing, and you know it,” John folded his thickly muscled arms across his chest in vexation, wishing that he had proper clothing so he could be properly cross.

“You would be dead without me, mine own little human, mine own John Watson. If I had not found you, if I had not given you your precious dry air, you would be naught but bones. I feed you. I protect you,” Somewhere along the line, Sherlock's voice hit a sinfully deep register, and suddenly John felt that he was the one being unreasonable. Sherlock had done so much for him. It wasn't Sherlock's fault that he didn't know what was and was not the right way to go about things.

John averted his gaze.

Sherlock drew nearer and made a little soft sound at him.

“Why do you treat Mycroft like that?” John reengaged with a non-sequitur. “He seems fond of you.”

Sherlock adapted to the conversational change without remark. He turned his pale, pale green eyes out to look at the ocean. “It is lies.”

“I don’t believe that,” replied John with certainty. He recognized sibling rivalry when he saw it. Undine or human, some things didn’t change.

“You told me that your men are solitary. And that Mycroft is trying to unify your people. Is that right?”

Sherlock rolled onto his back in the water and floated. He stared skyward. He looked like a discarded marble statue, but for the gossamer billow of his enormous white fins. John privately thought that a likeness of Sherlock would make a handsome figurehead on a frigate, although the artist would probably be alarmed at how very large, male, and decadently finned _real_ merfolk were (quite the opposite of buxom women with fish tails that were popular at the prow of ships).

“In his own way, Mycroft is as atypical of our kind as I. He enters the territory of other undine to form alliances, for one, and refuses to partake in the Riptide. Mycroft does nothing without a hidden motive. Nothing. Everything suits his grand design, nothing is unplanned! Even --” Sherlock stopped talking and looked irritated with himself.

John edged one foot into the water. “Even what, Sherlock?”

Sherlock turned his head in the gently lapping waves to look at John. A single black curl clung to his forehead, begging to be stroked into place. “You might have noticed that mine own brother is missing a fin?”

John nodded.

“When I was a fingerling, I wanted to investigate a human ship wreck. Unfortunately, the wreckage had settled in the territory of another of mine own kind. I was caught. He attacked me. Mycroft aggravated the situation further by... coming to mine own defense.”

John could see where this was going. “He lost his fin protecting you.”

Sherlock sniffed. “Yes. But as I said, Mycroft does nothing without a hidden motive. He killed the undine and claimed his own territory.”

John got the distinct feeling that Sherlock wasn't telling the whole story. “Nevertheless, it seems to me that your brother cares for you.”

“Enough,” Sherlock said softly. “I am bored by this talk of mine own brother. John. Come to me.”

A pale hand lifted imperiously. The skin of Sherlock’s exposed wrist was so fair that John could see the pale blue ribboning of veins just beneath the surface. John stepped into the water and took it. He pressed his lips against the delicate skin. Sherlock smiled a little. John kissed his way slowly up that long arm, tasting the salty-sweet skin.

Sherlock seemed pleased by this attention. “Come back to the grotto, John, where it is safe. Let me touch you. Let me feel your body against mine own,” Sherlock shuddered, then, clearly having just thought something particularly salacious: “I want to feel your _legs_ around me. So warm -- do you know how _warm_ you are, John? You are the sun contained by flesh.”

John stopped peppering kisses up Sherlock’s salty arm. “The sun, you say.”

“Yes,” sighed Sherlock, drawing John down into his wet embrace. “You are mine own small sun.”

No one had ever said something like that to him before. He slowly straddled Sherlock’s tight belly and cupped the undine’s face. _I can hardly keep up with him._ _His presence calls to me like nothing else. His hair, his eyes, his skin... his mind. What is happening to me?_

John felt a shift in the steely musculature he rode - like tectonic plates shifting pre-earthquake - before Sherlock’s eyes widened and he went rigid. “Ah! John. I just recalled. I have something for you. Wait here.”

The undine lifted John off effortlessly, and dove into the ocean in a hurricane of flashing white fins. John yelped at the flurry of motion and stumbled back onto shore, confused. He had been under the impression they were having a moment. “Wait. What? Sherlock?”

Sherlock had quite vanished.

_I definitely can't keep up with him._

“Rude,” John chided the empty shore.

~  ~

John made his way back to the ugly tree after Sherlock vanished. He could not afford to waste daylight waiting. The island was not so large. Sherlock would find him when he wanted to and, sure enough, John heard an overtone hum from the shoreline. The noise was nowhere near a full Song, just enough to make the hairs on the back of John's neck prickle. John waved his hand to show he'd heard. He was in the middle of tying empty coconut cups to the branches. He was running low on drinking water and hoped it would rain again soon.

Task complete, he went to Sherlock.

The undine did not even wait until John was properly close before tossing something at him. John caught it and did a double take. It was a knife. A good quality knife, too. Inlaid with mother-of-pearl, coral, and tortoiseshell, the ivory sheath showed a peacock in a blossoming tree. The hilt was carved ivory and the silver fittings were meticulously carved with inlaid colored cloisonné enamels. John drew the blade, and although it had some faint rust spotting at the base, it was otherwise pristine. He tested it on his thumb. It was wickedly sharp.

“This has to be worth a fortune. Where on earth did you acquire it?” 

Sherlock’s pale gaze tracked every flicker of emotion on John’s face rapaciously. “I found it. Do you like it?”

John swallowed over the lump in his throat. God help him, he did like the knife. Quite a lot. It was a beautifully crafted piece, but more than the aesthetic John appreciated its practicality. With a sharp knife, John would be able to gut fish properly, and he would be able to cut bark strips much more quickly. The days of using rocks and shells were history, and his chances for long-term survival on the island had just increased exponentially thanks to Sherlock’s gift.

“John?” a little wrinkle of impatience appeared on the bridge of Sherlock’s nose.

“What? Oh, yes. I do. Like it, I mean,” John coughed when excess saliva tried to go down the wrong tube. “It’s,” he interrupted himself coughing again and cursed his awkwardness in that moment. “Pardon. S’lovely, Sherlock. Thank you.”

The wrinkle smoothed out and was replaced by a serene, contented smile. John didn’t know why he said what he did next. Perhaps he just was on a roll with ruining things, lately: “I could hurt you with this, you know. It’s quite sharp.”

Sherlock’s aural fins twitched and the smile vanished. His voice took on a scientific detachment. “Would you?” 

“No! I mean. Probably not. It’s just that I’m surprised you’d trust me not to kill you.”

Sherlock rose up, water slicking down the gleaming black length of his scales. His shadow fell over John, and in that moment John felt exceptionally small. Sherlock’s expression was unreadable, but his pupils had taken on that atavistic squiggle.

“You’re welcome to try,” rumbled that deep baritone. “Though I must warn you; mine own kind is not so easily slain.”

John held up his hands in a placating gesture. “I won’t try to hurt you. And I’m grateful for the knife.”

Then John did something that was perhaps very brave, or perhaps very stupid. He tucked the sheathed knife into the waist of his kilt and stepped in close to Sherlock’s towering body. He rested his hands on the merman’s abdomen and stretched up to ghost a kiss against the curve of Sherlock’s jaw, which was as far up as he could reach.

“Thank you,” said John, and he came down from his tiptoes.

Sherlock cocked his head to the side and looked down at John with an unreadable expression. When he spoke at last, his voice was so low that John felt it more as a vibration in his spine than he heard it with his ears. “Come back to mine own nest.”

God help him, John actually hesitated. The tension was thick enough to cut and serve on fine china. “I can’t,” replied John at last, and even to his own ears John sounded strangled with regret. He moved to step out from beneath Sherlock but was stopped by a firm grip beneath his chin. The line of the undine’s mouth went hard.

“You think you are clever? Extorting promises so that I do not steal you away. It will only take once. Perhaps I should expedite this tiresome process and take you back, promises be damned.”

To emphasize his last point, Sherlock pressed up underneath John’s chin and nearly lifted the sailor clean out of the water in a sobering demonstration of strength. 

“I-If you do that, you won’t be able to Sing anymore,” gasped John through his creaking jaw, hands scrabbling up to grasp Sherlock’s unyielding wrist in an effort to relieve his jaw of strain. “Or control the waves.”

Sherlock sneered. He released John with a flick of his wrist, glaring as John stumbled back and flexed his aching jaw. 

“Mycroft told you entirely too much."

He ignored John’s bristling body language and eeled in close, skating the flat of his palms down John’s biceps. The undine’s other hand stroked down John’s body and lazily cupped his groin. He held John with absentminded confidence in his ownership -- as though John’s body was present exclusively for his entertainment, and it was natural and correct to be manhandling him.

John, god help him, felt arousal flare. There was something freeing about surrendering himself to Sherlock’s dark whimsy. He could relinquish control and be absolved of guilt, for if anything came to pass it would not be John’s fault. Sherlock squeezed him through the fabric of his kilt. “Hnnn, Sherlock. Sherlock, listen. I want to make a bargain with you.”

The hand on his engine stilled, and then fell away as Sherlock leaned back to study him. “A bargain.”

“Yes. I want your word that you will not harm me or try to trap me in your nest. I would be much keener on going back with you if I knew I would be allowed to come and go as I pleased.” It was true. John would have no qualms about spending time in Sherlock’s presence, if it didn’t mean boredom alone in the small cave with nothing to stimulate his mind. John had not forgotten how Sherlock had abandoned him for days during the storms, showing up only to briefly see that he had water and food.

Sherlock folded his lean arms over his chest and tilted his head to the side, studying John from beneath a tumble of dark curls. “You wish to come to mine own nest?”

“Well, it is much warmer there than it is under the tree at night,” John admitted, and he flashed a grin at Sherlock. He figured it didn’t hurt to lay on the charm if it helped his cause.

Sherlock’s pale eyes glittered with amusement. “And what would you offer in return?”

Oh, lord.

It was now or never. If he misworded this that would be the end of it. Sherlock would surely exploit any loophole John left. Thankfully, John had been ruminating on this for a while and was confident of his diplomacy. “One favor from me. Anything.”

The waves hiccuped around the sudden excited twitch of the undine’s great black-and-white tail. John held up one finger in a mute request for patience. “I’m not through. I offer _one_ favor in exchange for the aforementioned degree of freedom, and my obedience at that time only. The only stipulation I will set is that you cannot use my favor to bind me to your nest.”

Sherlock’s pointed teeth clicked together. “It is not enough.”

John’s heart sank.

“I need more than just your word, John Watson.”

John felt a frisson of anger lash, a cat’s tail, in his breast. How dare Sherlock? John had naught but the skin on his back, and apparently the greedy undine would have that, too. John prepared to say something uncivil. But then Sherlock’s webbed hand reached out and lifted the small leather bag around his neck.

“This.”

John faltered. “What about it?”

“I will accept the contents of this pouch as collateral.”

With those words, John’s world shrunk as though viewed through a pinhole. 

“I can’t remember the last time I took this off,” said John.

The undine said nothing.

There was a certain amount of luck involved in surviving as long as John had, and with time the contents of the pouch had become symbolic of John’s own hardiness. John knew he was being silly. It was just a token. A talisman, really, and it only held the importance that he gave it. If he let Sherlock have it, plus a single favor, John would no longer have to fear for his freedom in the ocean. He looked forward to the potential for a warm night’s sleep, for the sheltered grotto was infinitely preferable to the ugly tree’s dubious comfort. Good sleep would be worth the negotiations with Sherlock.

“Very well. Let’s do this, then. You promise first.”

John was mortified to discover this his hand was shaking. He forced himself not to think about what Sherlock might ask for his favor, for that way lay nightmares and arousal. Sherlock canted his head to the side, and his voice when he spoke had a resonance to it that hinted at his supernatural Song.

“I promise not to harm you or forcibly keep you in mine own nest,” Sherlock spoke so easily that John’s suspicion was aroused, and he sought loopholes in the undine’s promise frantically. Was there something he had forgotten? Why was he so calm? Sherlock raised his eyebrows at John as if to say ‘get on with it’. John swallowed.

“I promise that you shall have one favor from me, and this,” John ducked out from the leather loop around his neck. The pouch was so old that the leather had become buttery soft. John didn’t need to see his own reflection to know that a thin collar of untanned, white skin circled his neck. He curled his fingers around the hard weight of the lucky charm inside. What if his luck turned when he gave it away? What if giving it to Sherlock rescinded all of John’s hard-earned luck? Was he making the wrong decision?

Sherlock’s rib-gills had stopped flexing and he had gone terribly still.

John slapped the pouch into Sherlock's waiting hand.His throat was tight. He couldn’t speak if he had wanted to. Sherlock folded his long, webbed fingers around the bag and the tension broke for

it was done.

The moment the exchange was finished, something eerie occurred. All of the ambient noises of the ocean went silent. John was so accustomed to the constant roar of the surf and gull cries that their absence was startling. Sun gleamed off of the curve of Sherlock’s high cheekbone and as John watched his expression slowly transformed into a smirk.

John was afraid.

~  ~

* _Mycroft's design is based off of a[lionfish](http://safespear.poweredbyindigo.com/images/lionfish_lg.jpg)._

**Notes for the Chapter:**

> Let's see, I keep forgetting to mention that I have a [tumblr](http://jinglebell-fic.tumblr.com/) which you must check for current information on my update schedule (since I can't answer questions pertaining to that in the comments anymore). I'm doing Riptide Lover as one of my two rebel projects for [NanoWrimo](http://nanowrimo.org/participants/jinglebell-fic) this year, add me on there as a writing buddy if you are undertaking the challenge! Riptide Lover has [a playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I listen to while writing it, by the way. Feel free to suggest more songs. Don't forget to share your thoughts in the comments!


	8. Old Scars and New Bones

**Summary for the Chapter:**

> _In which John learns that the ocean can be a magical place - if you've got friends in high places._

**Notes for the Chapter:**

> Thanks to LapOtter for the consulting feels help, and to JP and Dee for betaing. The word for Sherlock’s people, undine, is pronounced “ _uhn - deen_ ”. Pronounce it as though you are a native French speaker, and francophones? As you were. 
> 
> Check [my tumblr](http://jinglebell-fic.tumblr.com/) for information on the update schedule, as I can no longer answer questions pertaining to that in the comments. Also, I added some more foreshadowing songs to [the playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I listen to while writing this, if you like.

A human being can only take a certain amount of fear before he becomes exhausted.

The body is not designed to hold onto terror for extended periods of time, and so John Watson found himself resuming life on the island with no small amount of pragmatism despite the odious bargain he had struck with Sherlock. Sherlock had vanished not long after they clinched the deal, and John hadn’t done much with the rest of his day -- his main accomplishment was spending his hours before sleep fashioning a crude rope scabbard for the ivory knife. Now, the knife was tied to his kilt. He refused to remove it even when he went to bed that night.

Sleep was slow to come, but when it did, John dreamt of wet skin and decadent scales. The morning sun, coupled with the solid weight of his cockstand proud in his kilt, woke him. John rolled onto his back and ground the heel of his palm against the root of his cock to alleviate the pressure. Visions of Sherlock swam in his head.

John’s hand smoothed down his own abdomen, underneath frayed fabric and past sandy curls, in order to give his cock a half-hearted pull. The sensation of his own fingers was... unengaging. John sucked his lower lip between his teeth and tried to tease himself. It was no use. He just felt ticklish. Exasperated, he slammed his palm violently onto the sand beside himself. John was lonely. Would he ever see another human being in his life? Was it his destiny to live out the rest of his days in solitude on a godforsaken island somewhere between Malta and London? John’s normally indomitable spirit was crushed by his seclusion.

_You’ve become morose, old boy._

No. This wasn't doing him any good, lying here wallowing in self-pity. He got up. He should better his situation. There was always some measure of practicality to see to on the island. Instead, John found himself drawn toward further violence: smashing coconuts open, and then not bothering to actually eat them. John kicked at a cracked shell, watching it skitter across the sands and roll into the surf.

Lashing out physically lost its appeal almost immediately, and so he sat down hard in the sand. John wrapped his arms around himself, folding his knees into his chest and squeezing as hard as he could, so hard that he felt his blood rush. He folded his grimy fingers into the still-healing scar on his palm and squeezed. He wanted to feel. He was starved for the touch of another human. He did not want to spend into the apathetic curl of his own hand for the umpteenth time.

He missed people. He missed the ambient noise of life on the frigate; the sound of restless feet on briny floorboards, the sound of coughing, of breathing, sneezing, and scattered laughter. He missed the sound of other human voices.

And now he was here. A bound, solitary existence, nothing new, nothing changing, and nothing to interact with but the bloody sea and the great fishy git within it. It was enough to drive a man mad. The transition from life on board a busy ship to a solitary existence was difficult. _Come on, Watson. You’ve survived worse - you’ve even been shot._ His hand flew reflexively to his throat, where John’s lucky charm would be safe in its pouch, but his necklace was gone. Sherlock had taken even that from him. John squeezed his eyes closed until white spots prickled behind his lids. 

That was the last straw.

He got to his feet, not bothering to brush the sand from his legs, and stalked down to the water. John made it in up to his neck by the time Sherlock appeared. The undine's face materialized in the waves, sleek head emerging cautiously. His seaglass eyes were bright with interest, flicking analytically over John's submerged body. The undine was affecting a neutral expression, but John suspected he was shamming; Sherlock’s flared gills betrayed predatory excitement.

“Sod this,” John spat.

Sherlock cocked his head to the side like a great, curious bird. A tumble of black curls spilled onto the surface of the water and floated over his cheek. He began to eel slowly around John, clearly intending to get in between him and the shore. John was was tired of playing this dangerous game with such arcane rules. As Sherlock inched by, John took control of the situation by pushing off the ocean floor hard, and diving over the heavy arch of the undine’s tail.

Sherlock watched in astonishment as John deliberately moved away from dry land.

“John?” Sherlock said incredulously. The premature note of triumph in his voice faltered.

“Sherlock!” John shouted over his shoulder, and spat out saltwater when a wave slapped his face. “I am going for a swim.”

And with that, John took in a deep breath and reminded himself that the trick was not to hoard the air, but to release it in a treacly trickle. He dove. The roar of the surf vanished and the brightness of the Mediterranean sun was diluted. Water rushed in John’s ears; he gave his eyes time to adjust to being open in sea water until he perceived Sherlock’s silhouette in pursuit. Sherlock was staring at him, intrigue evident by the cuttlefish-squiggle of his pupils.

The sight of those inhuman pupils reminded John of how he nearly drowned the night of the storm. His hands spasmed. _Calm down, old boy_ , John told himself. _You’ve swum in terrible conditions before, but the ocean favors you today. It’s naught but a swim._

So despite Sherlock's terrifying presence, John swam.

His style was brisk and efficient: powerful strokes and abbreviated kicks transporting him precisely to his intended destination. Air was too expensive a commodity to waste on extraneous flourish. In contrast, Sherlock underwater was poetry in motion. The undine was a dancer and his plumed fins the veils of his performance. Sherlock used his arms like slender white rudders to guide his course. He looked weightless, in flight.

The seabed was a vast and unending stretch of cream-colored dunes, peppered with debris. There were thousands of fish below the surface, and almost all of them too small and quick for John to look at with a hungry eye. They moved together like swirling clouds of autumn leaves. 

Sherlock swam in patient loops around John as he coasted along the bottom, raking his fingers through the sand just to experience the feeling. John perceived him indistinctly, like an artist’s impasto impressions of white and black upon a lapis canvas. Sherlock was so big that he made a current of his own wherever he swam; John could feel it lifting at him whenever the undine got close. John reached out to playfully grasp Sherlock’s spiny dorsal fin. Sherlock glanced over his shoulder but made no effort to dislodge him, and so it was in this way that John found himself being towed along.

If John had the air to spare, he would have laughed aloud in delight at the sudden speed. Did Sherlock feel like this all the time? Proud and fast and powerful under the ocean waves, ruler of an ancient and terrible domain? Hand over hand, John pulled himself up Sherlock’s long body until his hands were clasped around the undine's waist instead. Sherlock’s hands lit upon John’s forearms where they folded over the muscular plane of his belly, and John saw the vulnerable nape of the undine's neck as he looked down at where their fingers twined.

He could feel Sherlock’s rib gills flexing against his biceps, but John's own lungs burnt for air.

Would that he could swim with Sherlock forever without the troublesome need to breathe. It might be worth it. Perhaps John would not relinquish his hold, and perhaps then he would die. What if the last thing he ever saw was Sherlock’s curious face, peering down at him through a haze of blue? In his darker moments, John felt as though he was living on stolen time anyway; his survival of the ship accident had been _beyond_ improbable.

John smoothed his lips over Sherlock’s shoulder blade.

Sherlock turned around and leaned in close, eyes sparkling. John understood what was being offered; he sealed his lips to Sherlock’s and inhaled briny, life-giving air. Then John released Sherlock’s waist and pushed off with his feet on the heavy column of the undine's tail. Sherlock watched him go with a grin, and it was the brightest and most beautiful smile that John Watson had ever seen on any other living creature -- man, woman, or child. (The pointed teeth probably should have put John off more than they actually did.) His heart swelled with affection and John had to look away; he swam low and watched their cast shadows unite on the sea floor.

This submerged world was an experience unlike any other. No other human could ever dive beneath the waves so deeply without fearing for their life, John realized. _I suppose in this one way, I am a fortunate man indeed._

A familiar thready squeak sounded in the deep. John had been on the ocean long enough to recognize dolphins when he heard them, and he righted himself in the water to look for them. Sure enough, two curious dolphins approached from a distance, blurry shapes that John might have mistaken for more dangerous creatures had their squeaks and cries not preceded them. They split apart upon perceiving Sherlock, circling like shy puppies. 

John, for his part, found them incredible. He wanted to touch them, but the dolphins seemed reluctant to come close with Sherlock nearby. Sherlock's atavistic gaze flicked to John, assessing, and then he rolled his eyes and emitted a click followed by a high-pitched vocalization. The dolphins surged in close. John’s lungs were scalding. He didn’t _care,_ he wanted to touch the dolphins, but Sherlock paused him to transfer air. Only when John’s respiratory needs were met, did the undine set him loose.

John immediately reached for one of the bottlenoses, which butted its rostrum confidently into his palm. One of the pair was small. The other had a white scar on its melon.

 _I will call this little one Harriet, after my sister - and the one with the scar I shall call Michael Stamford_ , _after my friend,_ John thought to himself. John wasn't sure why he kept naming the living creatures he encountered. Perhaps if he named them they would not die.

John played with the dolphins. He couldn’t recall a time he had ever been felt quite like this. The closest approximation was when he was tarring the yardarms, nimble above a hard deck and sudden death. In his entire life, John had never experienced such a unique sense of relaxation and glee. The fear he had experienced upon making the bargain with Sherlock was remarkably absent.

The undine, for his part, seemed quietly captivated. He floated in the fringes of John’s vision like a hurricane gale in slow motion. He periodically interrupted John's aquatic nonsense to deliver air. The dolphins were markedly more cautious around Sherlock. At one point Harriet grew bold and swam up to flirt against the sybaritic white curtain of Sherlock’s plumage. The undine tolerated her proximity, but did not engage with her and she grew bored and went back to John. 

He did his best to keep up with them. They liked darting in and out and butting him with their beaks gently.

At one point, the dolphin he had privately dubbed Stamford swam below him, so John gripped its dorsal fin with both hands. The bottlenose squeaked with cetacean laughter and then they were off like a shot, John clinging to the rubbery thick fin and trying not to lose all of his air for laughing. Harriet swam in a spiral ringlet around them. John let Stamford drag him along until his lungs begged for relief -- and then he held on a moment longer still, because the spark of danger excited him.

Then he let go and rolled in the water, arms reaching out blindly. Immediately, Sherlock was there. He nuzzled into John’s space, nose cool against the corner of John's mouth the moment before their lips touched for the exchange of air. John tangled his fingers into the black cloud of Sherlock’s hair, thick and soft as pondweed. He could tell that he would have to surface for a proper breath soon.

John wriggled free of the undine’s grasp and swam out to say good-bye. Harriet gently took John’s hand in her beak and simply held it there. Stamford rolled in the water and pumped his belly up at John -- but Sherlock swiftly reprimanded that behavior with a vicious click. Stamford rubbed against Harriet instead. Then the dolphins took their leave, stripes of silver in the subtropical deep.

John could see the blurry light of the sun in the sky above. It was time. During their ascent, Sherlock swam close enough to make it obvious that he would not object to John hitching a ride, but John was stubborn and wanted to do it on his own. He broke the surface and floated on his back in the waves. The air tasted sweet and clean. The island was a verdant lump on the horizon, far away, but John felt no fear. Why should he be afraid? The most terrifying thing in the ocean was Sherlock, and the undine was _his_.

John’s cheeks stretched tight with joy. He felt Sherlock’s cheek nuzzle into his lumbar dip, and cool palms skate reverently over the curves of his arse and thighs. John snorted in bemusement. _You have no sense of propriety._  Sherlock’s hands stroked up John’s mostly-nude body and his head popped sleekly out of the water, breath cool on John's neck. He clicked twice. John still wasn’t sure what the clicking meant. He clicked back anyway, since Sherlock seemed to like it when he did.

Sherlock's eyes glittered with uncommon good humor. "Pft."

“What?” John asked, feigning offense. “My undine accent not good enough for you? Hm?”

“It’s a bit amateur,” Sherlock informed him gravely.

“Git!” John laughed and scooped water at Sherlock’s face, but the undine did not flinch at all -- in fact, he didn’t even blink, for his transparent eyelids were well-adapted to the salty spray of his preferred clime. _Git_ , John thought again, emphatically. They regarded each other. John, for his part, was amazed that Sherlock was still smiling.

“You are not afraid of the deep ocean?” Sherlock’s baritone seemed fuller, somehow, in the water.

“I’m afraid,” John admitted. "I just won't stop living because of it."

“There are more dangers in the ocean than your own human mind can comprehend,” the undine warned.

“Well. Begging your pardon, Sherlock, but _you’re_ the most dangerous thing I’ve ever encountered, and I’ve been on the ocean for nineteen years. Nineteen. If you’re with me, I expect I’ll be fine,” John’s ears went pink.

He hadn’t meant for that to come out sounding quite so intimate. Sherlock preened, tucking his chin and gazing at John from beneath a thick lace of black lashes. John felt the heavy curtain of Sherlock’s fins fold lightly around his legs under the water.

“And you are not afraid of me?” This inquiry was put tentatively.

John realized his answer could be catalyst or impediment to the progression of their acquaintanceship, so he gave it thought. Was he really afraid of Sherlock? The merman was inherently hazardous, but it was not unnavigable. John had adapted quickly to the abstruse rules of undine existence. He suspected that his destiny was now intertwined with Sherlock’s. He might not yet understand how, but he was accustomed to navigating unpredictable waters. He refused to let anxiety over some supernatural promise inhibit him.

Sherlock’s fins stroked against his legs, summoning John from his introspection.

“I don’t know if I am afraid of you,” John said at last. It was the truth. He reached out and brushed his fingers over the side of Sherlock’s face. His heart skipped a beat when Sherlock leaned his cheek into John’s palm, eyelids fluttering to half-mast.

“John,” breathed Sherlock. “I wish to show you something. Hold me now.”

Well, John wasn't going to protest that particular request. They maneuvered until John was draped over Sherlock’s slender white back, arms looped around his neck; he did not doubt the undine’s ability to carry his weight for an instant.

“Where are we going?” John spoke directly into a cartilaginous ear fin. He resisted the urge to suck the nubbed tip into his mouth -- a task made more difficult when Sherlock began to ferry him along without answering. 

They made good time out into the ocean. The noonday sun was blinding white, and John squinted gamely out at the horizon where he could see a distant murky land mass.  _Another island?!_ John shifted excitedly, tightening his fingers into the flat muscles of Sherlock’s chest. He craned his neck in order to peer over his own shoulder at Sherlock’s island. It was but a foggy shadow behind them. John looked forward, and to his surprise found that they had already nearly come upon this second island -- no, _islet_. 

It was a mere sandspit peeking out of the waves. But for the fact it was bristling with foliage, it would have been thoroughly unremarkable. There were so many hardy little trees  bunched together in the middle of this bizarre little islet that it was quite impossible to see the sea on the other side, and more coconuts studded the sand here than back on Sherlock's island. Was this where all the incongruous drupes were coming from? 

The most intriguing thing on the islet was a wooden dinghy. The boat was sun-bleached and old, and half buried in the sand far down the beach.

John inhaled sharply.

_A boat. Sweet Mary, it’s a boat. Is it still functional? Could I use it to escape? I cannot let Sherlock know that I’ve seen it._

Sherlock shifted beneath John as the water shallowed. John sprang free and sloshed forward until his feet sunk into hot sand. The dry land felt good after swimming for so long. He shaded his vision with his hand and watched as Sherlock made his way up onto the shoreline. He was careful not to so much as glance at the dinghy down the shoreline, for fear of drawing Sherlock’s attention to it.

Sherlock hesitated for a moment, glancing up at John.

Then he heaved himself onto the dry land and locomoted efficiently, if somewhat serpentinely, inland. His gills fluttered in an undine blush. John could see that he was self-conscious of his appearance whilst out of his element. His slippery white back was to John, dark hair curling wetly against his exposed nape. Vulnerable.

John’s hand drifted thoughtfully to the ivory knife where it hung against his hip.

He could do it. Sherlock looked smaller on land. If he was quick, John could draw the knife and be on the undine before he could protect himself. He would cut Sherlock’s throat. He had killed plenty of livestock at sea. The trick was to dig the blade in deeper than you thought you needed to, and pull firmly outwards with no hesitation.

John remembered when he had slaughtered his first goat, at the age of fourteen. He had botched the job entirely, slitting shallowly across the poor beast’s neck. Both he and the goat panicked, and this resulted in an undignified chase across the blood-slick deck. That was years ago, and John had killed hundreds of livestock since.

John crept silently across the sand.

Sherlock’s back stiffened and he turned his face sharply to stare at John in profile. His rib gills had sealed tightly closed to prevent sand from entering. John stepped slowly over the heavy length of Sherlock’s tail, careful not to tread on the white carpet of the merman’s fins. Sherlock had gone very still. John noticed how he struggled not to look directly at the knife hanging at John's hip, as though John wasn't already thinking of it.

John sank to his knees astride Sherlock’s jet-black tail, and bent over the undine’s back. He pressed his lips against the wet curve of Sherlock’s shoulder blade, skated his palms over his arms.

“You’re beautiful, you’re _beautiful_ , so bloody beautiful,” John whispered, nuzzling his nose into the dip of Sherlock’s spine and inhaling of that salt-sweet skin. Sherlock was trembling slightly beneath him, breath coming out in shallow staccato gusts, and John regretted that. He spoke soothingly against the bony curve of Sherlock’s shoulder blade. “Didn’t mean to give you a fright. I wouldn’t hurt you, Sherlock.”

Sherlock sneered. “I’m not afraid. Why should I be afraid of you, human? Land or water, I can kill you."

John kissed his way up the bumps of Sherlock’s spine and came to rest with his chin on the undine's shoulder. Gills flexed rapidly against his whiskers.

“Of course you could,” John said indulgently. “Now, what did you want to show me?”

Sherlock was remarkably tolerant of John laying atop him in the sand. He pointed at some boulders before them. “It will go faster if you do as I instruct, John. Go to the largest rock and lift it up."

John did as he was bid. The rock in question was huge and flat, and had to weigh over a hundred kilos. He hooked his fingers under the sandy lip of the boulder and brought all of his strength to bear. The tendons stood out in stark relief on his neck, and sweat trickled down his spine. His arms burned.

“Put your back into it,” suggested Sherlock saucily.

John told him to sod off, which came out sounding more like, “Hrrrrrnnnngh!” The rock sucked free of the damp sand at last and John groaned and hauled it aside, uncovering what was unmistakably a coffin.

John shouted aloud in horror.

Sherlock was laughing in that reserved undine way of his. “Open it, John.”

“Is there a body inside!?” cried John.

“No, just a skeleton. Open it.”

John stared at the undine. He looked back at the coffin. Then back to Sherlock, who had pillowed his chin on his palms and was regarding him in silence. He cut quite a picture there on the white sand of the tiny islet, his tail a black inkspill and the plumed fins sprouting from it as bright as new linen.

John sighed. He knelt by the coffin and brushed sand off the embellished lid. “How did you come by a coffin?”

Sherlock was eager to explain. “Is that what it's called? Interesting. I found this  _coffin_ in a small boat floating in mine own waters, twenty years ago. It makes excellent storage for mine own collection. I decided to keep the corpse as well,” A pause. Then, conspiratorially, “I like to call her ‘Pearl’.”

John laughed and tried to cover his gallows amusement by shaking his head. “Sherlock, this person was male.”

“Hm.”

“Yes. His name was --” John squinted at the oxidized copper nameplate and read, “Captain Algernon Portnay Kirk -- of the British Fusiliers. Blimey! I wonder what he was doing this far from home.”

“Not my concern. He’s mine, now, and I shall call him whatever I like. He cannot stop me.”

“I suppose not,” granted John. He opened the coffin and hoped he wasn’t going to hell.

John gasped. The skeleton of Algernon Portnay Kirk lay half-buried by a veritable blanket of treasure. The skeleton was old and completely devoid of flesh, although some dark hair clung stubbornly to its scalp. Coins spilled decadently over the coffin lip: gold guineas, silver seige ingots from Malta, Spanish and Sicilian dollars, and nothing of lesser value than a sovereign. Someone had shoved two nectarine-sized jewels into the eye sockets, an opal and a ruby respectively, and more cut jewels glittered in the shadow John’s body cast as he leaned over the coffin in unadulterated astonishment.

“My god. You have _actual buried treasure_.”

Sherlock was eating up John’s reaction. “Keenly observed.”

“Is this where you got my knife?” John asked, already knowing the answer.

Sherlock smiled and propped his chin on his palm.

John investigated the hoard. It was a ludicrous caricature of wealth. In addition to the coins, rubies, emeralds, and loops of pearls, there was a golden plate with matching cutlery, several small jewelry boxes containing silver earrings and a functioning compass (with only a small crack in the glass), an ornate sterling crucifix on a chain, a water-damaged copy of the Holy Bible, and a violin case. A dusty bottle of some unidentifiable liquor was nestled in the crook of the skeleton’s arm. And the skeleton himself wore the mess dress tunic of the British Fusiliers in red wool melton. The shoulder cords and all of the original embroidery were in place, the ensemble completed by white linen trousers tucked into black boots.

John’s thoughts erred on the morbid. “How did he not rot into his clothes?”

“The rate of human decomposition upon dry land had long been a hole in mine own personal research. Bodies are swiftly disposed of in the ocean, so, John, you might imagine my excitement upon discovering a human corpse --"

John picked up a gem-encrusted chalice. The sunlight glinted off of the edge like something in a story book. “So you took Captain Kirk here out of his coffin to watch him rot.”

“Verily so.”

John was rather amazed that Sherlock had bothered to redress Algernon Portnay Kirk’s body at all after his experiment. John moved the skeleton’s arm aside. Some natural objects were mixed in amongst the manufactured ones. There were pink and black natural pearls, opals, coral, and a fist-sized chunk of petrified wood, so glossy that John could see his own reflection in it. John sat back on his heels and wiped sweat from his brow. He could feel a sunburn forming on his shoulders.

“I can say honestly that this is one of the most spectacular things I have ever seen. Sherlock, this is incredible. Do you know how much these coins are _worth_? A man could retire several times over with half of this.”

Sherlock sat up in the sand, tight muscles of his abdomen flexing handsomely with the motion. “Do you like it?”

“It’s impressive,” John granted. _And most of it is useless to me._  He sighed and placed the chunk of petrified wood into the crook of Algernon’s elbow. “It must have taken you years to find all this.”

Sherlock’s eyes narrowed. “It did -- but that is not what I asked, John Watson. Do you like it?”

John raised his eyebrows in bemusement. “I do.”

The corner of Sherlock’s mouth drew up with pleasure. “Then you may take anything you wish from it." The significance of this offer was not lost on John; this hoard was clearly a labor of love and many years.

“I couldn’t, Sherlock, I --” but the undine looked sharply at him. John nearly bit his own tongue in surprise, seeing that he was on the precipice of offending Sherlock deeply. “I mean, I’m very grateful. Thank you.”

He sunk his hands into the gold coins. Sherlock relaxed, gills smoothing against his long neck. _Apparently, refusing a gift is a deep insult to him_. John separated a pile of things he thought might be useful: the compass, the plate and cutlery, and what was very obviously a woman’s hand mirror. He agonized over the bottle of booze, and ended up deciding to leave it. Best not to strip Algernon of his last earthly delight.

Task complete, he looked at Sherlock, who cast an appraising eye over John’s selection. “Mm. That’s all you want?”

“Money is of no use to me on the island,” John said darkly.  _That dinghy, on the other hand..._

Sherlock’s gaze flicked from where it had been resting upon John’s hands (which were, in turn, fiddling with the mirror handle) and up to John’s eyes. “Take the garments.”

John had to swallow a surge of bile that rose in his throat at the idea of wearing a corpse’s clothes. Did Sherlock want to play dress-up with all humans he came across, dead or alive? Still, desperate circumstances truncated his gut refusal, because new clothing was a resource he was unlikely to encounter again. John looked down at the skeleton. Its jaw was a bit lopsided, but it otherwise looked about as peaceful as a skeleton with jewel-eyes could. And the clothes were of a fine, if outdated, make. 

In the end, it was the boots that decided it.

John thanked the heavens that his feet were on the small side for a man; the boots of Algernon Portnay Kirk fit with wiggle room to spare. If he ignored the musty dead salt smell he could almost pretend they were made for him. Ten minutes later saw a naked skeleton, and John fastening the last dapper brass button beneath his throat. The red melton mess coat was a tight around John’s biceps and chest, but as long as John didn’t flex overmuch he figured the garment would hold. The linen trousers fit very well. 

John straightened his posture. There was something humanizing about being clothed. It made him feel like a proper civilized bloke. John scrubbed his hand over his whiskery face and winced. Almost. He was past the itchy stage of growth and long into full beard.

John turned to speak to Sherlock, and what he saw there caused his words to die in his mouth. The undine was sitting up on the beach, his hair dry now and a soft tangle of dark curls about his ethereal face. His eyes were impossibly soft.

“Sherlock…”

Just like that, the spell was broken. Sherlock's expression lost its fond vulnerability and was back to unreadable.

“John. The hour grows late, and the sea capricious. I would have us back by nightfall,” the undine pushed himself briskly back into the water and submerged his rib gills with a soft moan of relief, a sound that went straight to John’s cock.

“Ah. Right. Let me just.”

John crouched back over the coffin, arranging the treasures around the skeleton so that the lid would fit. He supposed there was something a bit wrong with him, that touching another man’s bones did not bother him as much as perhaps it ought. When John tried to close the lid, it thumped against the neck of the violin case. He was struck with a sudden curious inspiration, and he took the case out of the coffin. It was weighty.

“John.”

“Coming, coming.” John closed the coffin lid and reset the boulder. Sweating, he rolled his pile of loot into his tattered kilt, which he now used as a makeshift bag. _Whoever invented the shirt was a genius._   _Who would have thought a simple shirt would serve so many functions?_ He tied the shirt arms that his new treasures would not slip free, and gripped the violin case firmly by the thin metal handle.

He was ready - but there was one last order of business. He said to the boulder: “Right. Algernon. Er. Captain. I’d like to think you were a good man in life. You probably didn’t deserve to be posthumously robbed. Or kept in a merman's collection. So please don’t haunt -- uh, that is… thank you. For the clothes.”

“ _JOHN!”_

John jumped. He turned and was halfway across the sand when he found himself unable to resist one last superstition. “Rest in peace, Captain.”

John marched out into the ocean with his haul until he was submerged to the neck. It was a shame to wet his new garments, but there was no other plausible way to transport them. It wasn't as though merfolk came equipped with luggage trunks. The sun was setting, now, painting the seascape in shades of pastel orange, carmine, and gold. The satin weight of Sherlock’s fins brushed John’s arse and thighs, his only warning before a slender white back presented itself. John clasped him.

“Must you take this? It will slow us.” Sherlock rumbled, rattling the tips of his claws impatiently upon the hard leather of the violin case.

John hesitated. “I thought -”

“Never mind. Hold me.” Sherlock’s body became tense, then, and John’s hair prickled as some kind of energy bristled up through the undine’s body. Then, a strong current manifested around them and Sherlock rode it like a gull on the wind. There was no doubt in John’s mind that the undine had something to do with the sudden change in the water. In order to prevent the violin case from getting too wet, John had to waste an entire hand on holding it on top of his head. (He did not even want to contemplate how ridiculous this probably looked.)

John craned his neck to watch as the islet of bone shrunk into the saffron sky, and with it the old dinghy -- which held more value to John than any of the guineas or jewels in the coffin.

If only the islet was not so far away.

~  ~

It was night.

John sat upon the flat rock in the grotto, finishing up a fish and coconut for dinner. He was exhausted from diving all day, and there was pleasure to be had in merely having his lungs above the waterline. Sherlock was swimming restlessly around the rock. His wet head broke the surface occasionally in order to indulge his neuroticism that John was still present. John didn't have the energy to remark on the undine's neuroticism.

The Captain’s ensemble was laid out to dry on the first level of the flat ziggurat steps. John’s treasures were stacked neatly next to it, muzzy shapes in the dark. John was back in his makeshift kilt. The new garb was nice, but he had become accustomed to the maneuverability of the shirt tied about his hips. He sucked some coconut milk from his fingers and flopped back on the flat rock.

The grotto was so pleasantly warm. No wind assaulted him, here, and no driftwood would knock down suddenly in the night and startle him. Although the rock was not as forgiving as the sand, John preferred it. He wagered he could weave a thin mattress out of palm fronds. He stared up through the skylight of the cavern roof.

Stars twinkled.

“What are you thinking about?” Sherlock asked suddenly, baritone echoing softly in the cave.

John’s eyes had started to fall slowly closed as slumber crept in upon him. “Mmm.”

“John?” Sherlock’s voice was closer now.

“Fronds,” mumbled John, shifting slightly to fold his arms beneath his head like a pillow. “Just fronds.”

There was a _splipping_ noise in the water to John’s right. John opened his eyes a crack. Sherlock was leaning his forearms on the edge of the rock and gazing at him. The starlight made the water droplets in his hair glitter. John closed his eyes once more. He couldn’t even be arsed to care that a capricious creature of legend was probably going to watch him sleep.

A thought occurred to him. “D’you even sleep?”

“Yes,” replied Sherlock, and his voice sounded different, somehow -- almost like two people were speaking at once. It was relaxing.

“Well, I haven’t ever _seen_ you sleep,” drawled John.

Sherlock chuckled. “I sleep right here. In the waters in mine own nest, and sometimes upon this very rock.”

John inclined his chin slightly to show he had heard. The effort to vocalize a response was too much for his drowsy brain. After what felt like an eternity, John remembered what he wanted to say. He was so very muzzy with the onset of sleep that he hadn’t any eloquence to spare, but he wanted to get the thought out now, with the shield of darkness: “Thank you.”

There was no reply.

 _Oh well,_ thought John. He tucked his face into the relaxed cushion of his own bicep. A beat passed. John felt cool wet fingers stroke back his hair. The needle-tips of Sherlock’s claws trailed carefully over his skin, leaving prickled tracks of goosebumps in their wake. Sherlock’s hand came to rest upon the gnarled white scar tissue on John’s front shoulder, where it was stretching visibly with the position of his arm beneath his head. On display.

Anxiety pulled John awake and he opened his eyes to find the undine staring evenly at him.

John was a bit unnerved. Sherlock’s eyes were unlike anything he had ever seen -- sometimes, so very close to human that if John squinted and let the rest of the merman turn into a blur, he could imagine that it was another bloke he was talking to, on some gravelly London shore. Other times, John was reminded keenly of how farcical this situation was. Tonight, further evidence of the undine’s absent humanity presented itself in the halfpenny gleam of his irises in the dark.*

“You shouldn’t have survived,” Sherlock said quietly. His claw traced the ravaged rim of John’s old wound. John shuddered and said nothing. He had a feeling that Sherlock was working something out for himself.

“I looked inside the bag last night,” Sherlock confessed. John had expected this.

“Why do you keep it? Why does a lump of metal that almost killed you hold such significance?”

“It’s my lucky charm.”

Sherlock, rather than saying, ‘It’s just a bullet’ or chastising John for his superstition, nodded his head in understanding. “Is he dead?”

“What?”

“The man who tried to kill you. Is he dead?”

“ _She._ And no, she is not. I pray.”

Sherlock perked up. “ _She_?”

“My sister. Harriet.”

Sherlock sat back in astonishment, water sloshing. He removed his hand from John’s scar as though he had been burnt. He seemed so genuinely surprised by this that John immediately came to his sister’s defense, all thoughts of sleep vanished. Yes, Harriet had shot him. But the situation had been out of her control. John did not blame her for an instant. A fierce surge of protectiveness rose within him.

“Now you listen here, Sherlock. It was not Harriet’s fault. Harriet Watson is a saint, and you make no mistake. If that soldier hadn’t impugned upon --”

John sat, suddenly roiling with unpleasant memories of that night eight years ago. It was definitely the worst night of his life, worse, even, than the night he had been tossed over the rails of the _HMS Endymion_ and into Sherlock’s clutches. Even now, he remembered the burn of cruel metal sinking into his body, a hot knife through butter. He remembered the weeks of agony that followed. He remembered howling in pain as the infection ravaged him. They had to strap him to the bed to keep him from harming himself. John had begged for them to kill him. " _Please God, let me die_ ," he had prayed. In hindsight, John regretted that, but the pain had turned him small and stupid.

His scar throbbed.

He gasped for breath.

He couldn’t get enough air.

He couldn’t _breathe_.

“John. You are alive. You are well,” Sherlock’s deep voice had taken on an overtone hum, and somewhere behind the veneer of panic John realized that the undine was using his Singing ability to imbue his voice with a supernatural compulsion. “I am here. No one will hurt you, John. I will kill them.”

It was that last remark, spoken with such certainty, that penetrated the haze of John’s memories. Surprised, John let out a hard bark of laughter. His embryonic panic receded and, after a spell, he was able to speak. But he wanted to make sure that the undine understood one thing:

“It’s not Harriet’s fault,” John exhaled slowly through his nose. “That is. She was not in her right mind. At any rate, it is not something I wish to discuss further.”

Sherlock was humming quietly in his throat, a noise that John perceived on a cellular level rather an auditory one. It soothed him. John slowly lay back down upon the rock, and exhaled gustily. He felt hollow. Between the long swim in the open ocean and the perusal of painful memories, John's physical and mental reserves were tapped. Sherlock resumed his slow circle around the flat rock.

Slumber knocked tentatively upon his door once more.

The humming continued.

John slept.

~  ~

_* Sherlock, like many (but not all!) undine, has[tapteum lucidum](http://en.wikipedia.org/wiki/Tapetum_lucidum)._

**Notes for the Chapter:**

> I invite you all to discuss amongst yourselves in the comments the following psychological phenomena as they pertain to Riptide Lover: PTSD, capture-bonding, Stockholm syndrome, and Lima syndrome. ~professor spectacles manifest~


	9. Jonah

**Notes for the Chapter:**

> This chapter contains **graphic depictions of violence** and fictionalized harm of various creatures. If you’re a responsible reader, you have already read the tags and knew what to expect going in. Please be a responsible reader! Please check [my tumblr](http://www.jinglebellfic.tumblr.com) (URL now sans hyphen) for the update information, as I can no longer answer questions about that in the comments.
> 
> As an aside? I have no personal vendetta against seals, and I play entirely too much Dungeons & Dragons. Thank you to Dee, JP, and Red!

John woke to the gurgling vocalizations of monk seals.

The closest he’d been to seals was when the frigate had passed pods of them basking, so he recognized the sounds. They were much closer than he was accustomed to hearing, however, so John slid off of the flat rock and swam outside. He stood on his toes in the water alongside Sherlock, who was coiled there watching his lagoon. Fins brushed the back of John’s legs in acknowledgment.

In the morning light, Sherlock was breathtaking.

The undine’s torso was above water, and the spray of delicate onyx scales on Sherlock’s deltoids caught the light fetchingly. His abdomen was sleek with the musculature of a longtime swimmer, though lacking human landmarks such as nipples, or a navel. The narrow shutters of his rib gills flexed peek-a-boo. Since Sherlock’s attention was occupied, John let his gaze flick curiously to the merman’s inguen.

Tiny black scales grew larger the farther down Sherlock’s tail one looked. The mysterious pink slit that had manifested when they had kissed was nowhere to be seen. The undine’s pelvic fins were dormant; although these fins were just as pearl-white as the others, the anatomy was more solid. They were tipped with a minuscule white claw, almost like the finger of a bat.

John wondered if Sherlock could grip with them.

A gurgling bark from the lagoon startled John back into the present, and he reluctantly tore his gaze from Sherlock’s bewitching silhouette. Sure enough, a pod of monk seals had decided that the lagoon was the perfect place to sun themselves. Five animals were perched on the thin strip of the western shoal, grunting to each other.

John hid his yawn in his palm, tired but coming round from sleep. “Oh.”

Sherlock inclined his head, but his pale eyes were sharp on the seals.

Like a fat fur-covered sausage, one of the seals wriggled its way across the shoal to rub whiskers with another. It was a touching natural scene... but John’s stomach growled. It had been almost a month on the island now with a limited diet, and John craved two things above all else: fruit, and _red meat_. He wondered if he would be fast enough to catch one. They looked pretty slow up there on the shoal.

“Don’t,” Sherlock warned him.

John flushed. “I wasn’t -- !”

“You want to eat them. Don’t trouble yourself, you’ll never catch one.”

John turned in the water in order to glare at Sherlock. He kept his voice low. “I wasn’t going to hurt them.”

Sherlock arched an eyebrow but let the lie sit.

John understood why the monk seals had chosen to alight here. The cove was an ideal resting spot, with its protected shallow waters and flat spits of land. Sherlock slipped out into the turquoise water of the lagoon. The seals’ heads all popped up in unison, but they did not flee. One of the juveniles was curious. When Sherlock sidled up adjacent to the shoal, the seal leaned over to sniff where the dark cloud of the merman’s hair floated just below.

For a heartbeat, nothing happened. John honestly did not know what to expect.

Sherlock surged out of the water in a movement so rapid that he surprised John into losing his footing. He plunged under briefly and emerged spluttering. In the moment that John had been submerged, Sherlock had pounced upon one of the seals. Now he was holding the bleating, thrashing animal under his arm like a farmer with a ewe for slaughter. He looked over at John to make sure he was watching.

Then he broke its neck.

This started a chain of events: the seals dispersed, John felt a confusing mixture of elation ( _RED MEAT)_ and horror ( _it had been so peaceful),_  and Sherlock couldn't just leave it there, he whirled in the water and did something truly horrifying.

He Sang the seals.

John heard the harmonic resonance that wove several pitches at once and his body seized in remembered dread. It was evident that the intended audience for this Song was not John; the sailor was able to deny his own impulse to approach Sherlock. The seals were not so lucky.

“Oh god. No, Sherlock, _stop_  --!”

Sherlock did not stop. He continued to emit that low, pulsing wave of sound with its multiple layers braiding above and below his basso hum. John swore he could hear childlike voices harmonizing on the wind, odious in their innocence. The seals were compelled to Sherlock’s side. They foamed and shivered even as they strove to get physically closer to the undine.

“SHERLOCK, I SAID NO! STOP THIS WITCHERY!” roared John, sloshing out into the lagoon. He cursed the slow buoyancy of his steps.

Sherlock stroked a whining seal’s head and cast his inscrutable gaze upon John, who found it infuriating that the undine was able to speak normally, albeit at a louder volume, over his own Song.

“You do not need to hunt, John. I am capable of providing you with whatever you need.”

John saw red.

He breathed in, slowly. Held it. Then released. “Sherlock. Let them go.”

Sherlock eeled his head to the side.

John crunched his hands into white-knuckled fists. He figured he could get in a left-hook and possibly a quick jab with the right before the undine could subdue him, but before violence became necessary to make his point, Sherlock stopped Singing. The Song lingered on the wind like an echo as the seals escaped into the open ocean, a cacophony of distressed vocalizations soon the only evidence of their inauspicious visit. John was livid. His blood was fire, his voice ice.

“Do you know no compassion?” he spat. His pulse thumped in his jugular, a war drum.

Sherlock’s gills flared out warningly. “Do not impose upon me your own _human_ ideas --”

“It’s not about being human,” bellowed John, slapping his palm on the water’s surface. He took joy in the violence of the motion. “It’s about being decent! What you just did... it, it was the most cold-blooded, merciless, cruel, _senseless_ -”

“Careful, John.”

“I WILL NOT BE CAREFUL!” boomed John, surging forward in the water and into the undine’s space.

Sherlock held his ground, and he stared down his patrician nose as though John were behaving in a manner he found particularly amusing. This stoked the fire of John’s rage to new heights.

“You. I hate it when you do that, I absolutely loathe it. I have never seen something so, so _monstrous -_ ”

Sherlock’s shoulders tensed, and John knew he had said something wrong. John did not think of himself as a cruel person. Sensing that he had struck a nerve, he strove to regulate his volume - if not the content of his words.

“What you did just now is totally unacceptable, Sherlock.”

Sherlock reached out to stroke his face, and John flinched away furiously. The undine smirked and let his hand drop.

“I don’t understand. You wanted to hunt. Your own respiration rate increased and your own fingers clenched. You were trying to decide whether your own knife would be sufficient to bring it down,” Sherlock jiggled the dead weight of the seal body that was tucked under his arm in emphasis. “I expedited the process for you. I can bring you as many seals as you like.”

“It’s not about the seals!” snarled John.

Sherlock gave John the side-eye. “It isn’t?”

“I can’t deny that seal meat and its pelt would be useful. It’s about how you chose to hunt them! Killing a single animal for food is necessary. This seal was hunted justly,” John gestured to the game Sherlock held. “But the - the Singing? That is _not on_. You were terrifying them, Sherlock.”

“Why do I care if mine own prey is afraid before it dies? Those that cannot endure mine own will are weak. Those that out-think me shall live to see another day; they are wiser for the experience. As for the weak... they should be grateful to me.”

John cocked his head sharply to the side and squinted disbelievingly. “Grateful, you say.”

“Yes. Their sacrifice sustains mine own existence.”

John smacked his hand on the water’s surface again.

“No. No, that is not how life works. I don’t care that you’re a bloody merman --  _undine_ , I don’t care that you’re the most dangerous creature in these waters. Your strength puts you in a position of responsibility. You musn’t abuse it. Especially to poor dumb beasts!”

Sherlock stroked his thumb repetitively over the velvet fur of the dead seal. John wondered if it was a nervous gesture, for the undine’s face was unreadable.

“You sound like Mycroft. Would you have me starve myself?”

John scrubbed his hand over his face in frustration. The scar on his palm tingled. 

John guiltily remembered the first goat he had slaughtered. He dropped his gaze to the the seal flopping in the crook of Sherlock’s arm. Its soft, liquid-dark eyes reminded John of a cow. “No, I wouldn’t. Of course you deserve to hunt for survival. Just… do not let your prey suffer, yeah?”

“I listen... but I ask you this: if you were undine, and capable of the Song, would you use it?”

 _Would I use it..!_ John hadn’t actually given the situation thought from Sherlock’s perspective. It was a monumental effort to consider the undine’s point of view when his blood was hot with helpless rage. He slicked a wet hand back through his hair, which had fallen over his forehead and weighed his response.

It was the way of the ocean to kill or be killed. John knew this. But seeing Sherlock’s siren call surfaced recent memories of that night on the moonlit beach. Even the crabs had been drawn to Sherlock, marching like tiny crustacean soldiers called to war. John felt sympathy for the seals, yes, but more than that John experienced empathy. He had been there himself. He knew how it felt to become a mere passenger in his own body.

Wylie Clegg alighted upon the shoal and preened his feathers. Seeing old Wylie going about his affairs cooled John’s ire.

The corner of a gossamer fin tickled John’s calves. He jolted back into the present and realized that Sherlock was awaiting his response. “Look... I don’t know, Sherlock. You have to understand. I come from a completely different place, a different culture. London isn’t, that is, my kind would never -”

Sherlock’s gaze was sharp and bright as a diamond. “Your kind, you say. I have observed the cruelty and pettiness of man. Don’t be a hypocrite.”

He had a point.

“Do you find the notion that undine and a human could coexist impossible?”

John laughed harshly. “Of course it’s impossible. We’re too different, you and I.”

Sherlock’s arm tightened around the seal. John winced when he heard the muffled thump of a seal rib breaking. That sound clinched it. If he were back in London, John would have gone out for a brisk walk to clear his head. If he were back on the frigate, he would have voluntarily thrown himself in to hard physical labor. Here, there was only one way to take his mind off his conflicts.

“I want to go back to the island,” John said firmly.

Sherlock turned and tossed the seal onto the shoal. The body skidded limply to a halt in the gravel. The tide lapped quietly at its flippers. Sherlock shook out his hands as though he had just thrown out rubbish. “Then go. As promised, I will not forcibly keep you.”

John’s heart sunk with a dreadful realization.

This was the loophole.

 _This_ was why Sherlock had been willing to make the bargain. It was all wordplay and exploited verbiage. Sherlock had agreed not to prevent John from coming and going as he pleased, but the undine had never promised to help John with the reality of transportation. For a merman, swimming in and out of the cove was a walk in the park. For a human?  Not so much. The swim back to the island proper was not a journey easily undertaken. John’s prior success had been just as much luck as it had been skill.

Sherlock tossed his glossy curls and submerged. As if to demonstrate how easy it was for him to come and go as he pleased, the undine slipped into the open sea and abandoned John to his own devices. He didn’t even bother to say goodbye.

“Damn,” John said.

He was more irritated with himself than Sherlock.

From day one, Sherlock had made no secret of his iniquitousness. It was in his nature to be selfish. John had grown complacent with their successful negotiations, and he had chosen to play with fire. Now he was paying for it.  _Still, if this is the only loophole Sherlock found in our bargain, it is not so bad._ _It's not impossible to reach the island without Sherlock's help, merely risky._

And it was not in John’s temperament to balk at a little danger.

~  ~

John left the compass, dinner set, hand mirror, and violin case in the cave. Although he regretted leaving it, there was no way he would impede himself by wearing the British fusiliers uniform. The knife was secure against his hip, and that was the most important thing. He would show Sherlock. He didn’t need the undine for mobility, or food, or shelter.

He relied on no man but himself.

He was a good distance out in the water already, despite the choppy waves. The swim was not as smooth this time around; John’s limbs felt leaden already. He should have given himself more recovery time after the exertion of the day before, but he refused to turn back. So John began to hum. He could practically hear the voices of his mates belting out the familiar sea shanty in his mind:

_Oh, Nancy Dawson, Hi-oh!_

_Cheerly, man!_  

He focused on one stroke at a time, pulling himself stubbornly through the combers. His arms were steady metronomes.

_She robbed the Bo-sun Hi-oh!_

_Cheerly, man!_  

Pull. Pull. _Pull_. He could do this. He was not going to rest his arms, for to stop now would surely spell his doom.

_That was a caution, Hi-oh!_

_Cheerly, man - O! Haulee, Hi-oh,_

_Cheerly, man..!_  

John checked his progress and was surprised at how far out he had come. The island was a verdant lump, the craggy crown of the sea cave jutting a dark silhouette into the sky at one end. He had overshot the dangerous currents. Now, all that was left was to navigate back inland. He imagined the soft white beach. He could do this.

John looked to see if Wylie was still following him. Over the course of the past few weeks, the bird had taken to tailing John in the hopes of getting scraps of food. As it turned out, Wylie was out on the waves at some distance, bobbing like a buoy.

Something dreadful transpired, right there in the bright light of day:

The cormorant unfurled its wings to take hasty flight, but not quickly enough. Wylie was abruptly plucked underwater by a

_giant_

_mouth._

The ring of gleaming white teeth vanished into the foam as quickly as it had appeared. One moment, Wylie Clegg had been floating on the waves and preening himself, and the next, he was claimed by silent death. There hadn’t even been time for the bird to squawk, to cry out at the injustice of his anticlimactic end. John looked on in astonishment. _What the BLAZES was that? Oh sweet virgin Mary, what was THAT?_

A triangular fin rose up and sliced through the water toward him.

“You’ve got to be kidding,” John’s voice came out in an adolescent squeak.

His body flooded with adrenaline so quickly that he became light-headed. In the space of seconds, he was primed to fight or flee. He ducked his head under the waves to locate the threat, and what John Watson saw then would be a recurring theme in his nightmares for the rest of his life.

It was a monster.

There were some things that the human brain was not built to accept readily, and the existence of sea monsters was one of them. John’s brain stuttered to absorb the concept. If infinite malevolence could take a physical form, this creature would be it. It looked like the progenitor of a white shark, but here nature had run cruel and rampant. 

 _Leviathan_ , a voice in John’s mind quietly supplied, and then, bizarrely, recalled a passage from the Old Testament:

_Any hope of subduing it is false; the mere sight of it is overpowering._

The leviathan was far larger than any true shark, and its skin was so rough that plants and other flotsam had caught upon it. An entire small ecosystem had developed on the dorsal plane, slimy sea fronds billowing in the current. Feeder fish clung to its massive bulk as it swayed ponderously through the deep.

Its maw was large enough to swallow a horse whole, and was open to expose the ribbed white insides of its gullet and a carpet of needle-sharp teeth. The creature’s tail was a ludicrously-proportioned blade that brought to mind a thresher shark. It had abyss-colored eyes, which seemed to regard John with the acuity of a man. 

All told, it was the length of a canal boat.

It was heading slowly, inexorably, toward him. With great reticence John kicked to the surface to breathe.

“ _SHERLOOOOOOCK!”_ John bellowed. He gave the shout all the volume he possessed.

Then he went back under.

It would be foolish to turn his back, for there was no way he could hope to outpace it in the water. And John would be damned if he was going to be eaten mid-flight.  _Come on then_ , John thought. He drew the ivory knife, treading water. _I refuse to be your Jonah, although I don't think I will make it out of this alive._

The leviathan was fifteen meters and closing. The water rushed in his ears, and John felt curiously detached from his own body - as if he were the puppeteer of an exceptionally lifelike marionette. He honestly had no idea where to strike first, if he even had the opportunity. Perhaps on his way down its throat he could get in a good stab.

Then, Sherlock happened.

The undine manifested from the deep water, rocketing upward like a sleek bullet. He struck the leviathan from below, arms open to catch it in his steel embrace. The sound of their impact was muffled underwater. His strike was evidently not insignificant, for the ghastly shark convulsed and tore free, its rough hide sloughing the skin from Sherlock's forearms in a bloody plume. It swam in a circle around them.

The leviathan’s abyssal eyes were focused with skin-crawling specificity upon John, utterly disinterested in engaging with Sherlock.

It wanted _him_.

Sherlock’s hands flexed open, claws a ready gleam. He glanced over his shoulder at John. The undine shooed him in an clear _get out of here_ gesture. John didn’t need to be told twice. He kicked to the surface, sucked in a fresh breath, and began to swim like his life depended on it, because it did.

If someone had told John that at age thirty-two he would be swimming for his life whilst two sea titans engaged in mortal combat beneath the waves, he would have laughed. He would have bought them another pint, and told them to go on, tell us more. But this was his reality. A world where mermaids existed and leviathans roamed the Mediterranean sea with eyes that gleamed with humanlike intelligence.

John missed life on board the frigate. He didn’t know if his heart could keep up with any more of this mythological nonsense. A very basic part of him hoped that both Sherlock and the shark would kill each other.

Discarding these ultimately unhelpful thoughts, John pushed his tired body to the limit and past - ignoring the screaming protest of his muscles as he swam until an ominous feeling prickled up his spine.

John listened to his gut instinct flung himself sideways, a clumsy diagonal sink that probably saved his life, for the leviathan's tail was cutting about wildly, and had he not dodged, his legs might have been bludgeoned.

Sherlock had drawn the abomination’s attention, fins snapping like sails in a hurricane gale as he harried it with rapid strikes; his claws tore free strips of ancient flesh until the monster was inclined to prioritize him. There was a rusty cloud around them both, and too much happening at once to locate the wound.

John’s heart was in his throat. Sherlock was hurt. What if Sherlock died? It was easy to think of him as invincible. Until now, John hadn't known there was anything more frightful in the entire ocean than the undine. Sherlock certainly did nothing to dissuade from that perception, with all his talk of weak and strong. Sherlock, with his way of thinking, probably wouldn’t resent the leviathan even if it did kill him.

John saw a flash of red and white in his periphery.

He whirled in a cloud of anxious bubbles, worried that it was some new marine horror, but it turned out to be Sherlock’s brother. Mycroft’s decadent caudal plumage was flared out in a shivering threat as he shot beneath the leviathan and raked his venomous spines against its belly. 

That got its attention.

The leviathan hyperextended its jaw trying to bite Mycroft in two, and might have succeeded but for Sherlock flurrying suddenly in its face, and John missed the next bit because he needed air so he surfaced long enough to gulp it and notice in despair that the blood was darkening the water below, and it was impossible to see unless he was also submerged. He went under.

Sherlock seemed to be trying to grapple the shark. His tail curled partially around the creature's inflexible trunk, holding himself in place as he rent with his claws. Mycroft was up to his elbows in the leviathan's gill flesh, expression icy with concentration as he worked with Sherlock in fluid synchronicity to fill the sea with blood and chum. John could only look on in horror as the leviathan's jaws champed shut again and again, blindly searching for flesh, and it was only Sherlock's lightning reflexes that kept him a hair's breadth out of the range of those odious jaws. Time and time again he dodged bites that could bisect a horse, and he did so with a dancer's fluidity, stoking John’s suspense to greater and greater heights with every success.

Sherlock hooked his hands on the leviathan’s snout, and the other on its bottom jaw, catching it the instant before teeth would have pulverized him. Every single tendon in Sherlock's arms stood out with exertion, straining to prevent it from biting down. John thought he might be sick. This was the end. What would become of him if Sherlock died? Would that buy him enough time to escape himself? Why did the thought of Sherlock’s death trouble him so deeply? He needed to breathe, but he needed to see what would happen more.

Sherlock emitted noise at a pitch that John's human ears were not able to fully process, some kind of close-range subsonic bark that sent a visible ripple through the water. The behemoth shuddered, a full-body convulsion, and sagged in Sherlock's grip. The brothers looked at each other. Mycroft nodded sharply at Sherlock. He detached from the leviathan’s thoroughly pulped gills and swung out into the blue to watch at a distance. He was favoring his arm greatly.

Sherlock wasted no time. Perhaps his sonic assault was not a permanent solution. Tail windmilling, Sherlock flexed his arms and _ripped_ ; he gradually split the leviathan's jaws apart like unrolling a scroll. Every muscle in his back stood out in violent relief, as this feat seemed to require every ounce of the undine’s supernatural strength. John could hear the wet stretch and snap of ligaments being slowly and inexorably drawn apart, sounds that eventually terminated in a muffled crack of bone.

Sherlock’s expression was absolutely feral, teeth bared in fierce victory. John felt lightheaded. When was the last time he breathed?

Sherlock released the leviathan’s giant carcass to the caress of the current, where it slowly sank toward the seabed and the waiting schools of smaller sharks and fishes. John kicked to the surface to breathe. His thoughts raced. His body was drugged with adrenaline; his fingers and toes were almost entirely numb. The idea of going back below for even a second was abhorrent to him, but John needed to see what was happening. If only he had gills. He submerged and blinked until his eyes adjusted to the brine.

Mycroft and Sherlock were communicating.

The brothers had clasped forearms and their heads were bent close. Even at a distance, John could see their throats flexing, which was how he knew that they were making vocalizations inaudible to humans. Mycroft’s left shoulder seemed to be dislocated. Sherlock’s rib gills were wide open and flexing deeply with exertion. There was a great deal of blood befogging Sherlock’s fins. Both brothers’ hands – no, their _claws_ \- were sending blood up in the water, drifting toward the surface in sleepy spirals.

Mycroft looked disgusted. He said something to Sherlock, then - something that apparently the younger sibling did not like. Sherlock scowled. He replied and released his hold on Mycroft’s forearm. Then he made what was unmistakably a shooing gesture. Mycroft looked skyward as though beseeching god for patience.

Sherlock indicated John and said something urgently. (John wished he could disappear.) Mycroft considered this latest point with a slow tilt of his head.

They both turned to face John -- who flinched in existential terror and swam backwards. Mycroft dipped his chin carefully to John, who found himself automatically nodding back, and slowly took his leave, wounded arm hanging limp at his side. Sherlock stayed behind, bleeding as he watched John carefully from below. John was struck once again by Sherlock’s sheer size; he was an enormous creature with all of his fins and gills still flared out, dramatic white flags on his otherwise black tail. His hair was a black corona around the startling white of his face. After a moment, Sherlock lifted his hand to John.

Even though there were meters between them in the water, John flinched. Air escaped his nose, and Sherlock frowned and drew near.

John kicked upward, forced to surface for oxygen. He sucked in a breath as quickly as he could and prepared to dive back under, but it was too late. Strong, cool arms banded around John's waist, unyielding.

John shouted and thrashed.

Sherlock's arms tightened around him, and John fought him with everything he had, kicking out violently. He couldn't even see Sherlock through the sea foam and blood, the taste of fear acid on his tongue. Sherlock pinned John’s arms and began to drag him back inland, to the cave. John flailed and squirmed. Hell he even bit the protruding web of Sherlock's ear when it came within range... but Sherlock was too strong.

Despite John’s protests, he was dragged spluttering and howling through the waves and back into the shadow of the sea cave.

_~  ~ _

_* I added the sea shanty John sings to himself to the Riptide Lover playlist I like to listen to while I write.[The version I included](https://www.youtube.com/watch?v=jCUNJhPCuoQ) is actually from a game called Assassin’s Creed: Black Flag!_  

**Notes for the Chapter:**

> Two artistically inclined readers drew their wonderful interpretations of undine Sherlock! [Portrait](http://starshipspirk.tumblr.com/post/102685782113/i-did-a-quick-illustration-of-how-i-imagine) by Kaiju, and [Sherlock](http://the-child-of-night-and-day.tumblr.com/post/102162315185/on-lazy-days-with-johns-pouch-sherlock-fiddles) by child-of-night-and-day. Wow, great job! <3
> 
> Lastly, thanks to you all for bearing with the slow build nature of this tale. I have a rather epic (in the original, literary sense of the word) story I wish to tell, and I would rather take the time I need to do this _right_ than rush through to the ending prematurely. 
> 
> I hope you enjoy the voyage nonetheless. <3


	10. The Same Blood

**Notes for the Chapter:**

> There’s a bit of a carnal pyramid in this story, because that’s what I find sexiest. We start with handjobs and work our way up to penetrative sex and marine sex toys. Just so you have an idea of what’s coming, haha! There's a [playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I listen to while I write. Please check [my blog](http://jinglebellfic.tumblr.com/) for the update schedule, as I am no longer able to answer questions about that in the comments. There's a holiday schedule change coming up.

Sherlock wrestled him back into the familiar shade of the grotto, not stopping until they were deep inside, behind the flat rock where a narrow channel of water separated it from the back of the cave and its stone steps. A carpet of spongy green plants swayed in the current here and tickled John's bare legs. John's fear made him furious. Sherlock would not release him, and so John kicked the silken folds of the merman’s bleeding fins. Sherlock doubled over with a hiss and John wrested free.

He scrambled onto the giant ziggurat steps, where the treasures of Algernon Portnay Kirk were still neatly stacked. Almost knocking the violin case off the edge in his haste, John turned to snarlingly address his mythological companion. What in the name of god had just happened? He now had enough nightmare fodder for several lifetimes, thank you very much, but when he saw what he had abandoned below, John paused.

Sherlock’s long body was curled on the mattress of sea fronds, and his shoulders were hunched in a rictus of pain. Now that he was still, John could see that the beautiful flag of his adipose fin had been torn clean in two and shame shriveled John's ire.

“Oh… Sherlock,” he sank to his knees and planted his palms on the stone edge. “God, I’m -- I'm sorry.”

That morning they had argued. He had accused Sherlock of being without compassion, his behavior monstrous, and although he refused to back down on the point that Singing the seals had been cruel, John now came to acknowledge that his words had been too.

The truth of the matter was that Sherlock was capable of great valor. John had called for help, and the undine had unhesitatingly come to his defense. How did John repay him? By kicking him, and behaving as though the undine were contemptible.  _Heavens. I am the monster, here. Not him_.

John lowered himself into the water, careful not to step on Sherlock's plumage. Sherlock regarded him in labored silence. He drew his tail in close, a thick black coil. His breathing was shallow and urgent, still, and his fins had not yet quieted. The undine seemed to be coming down from the energetic high of battle, but when Sherlock spoke, his voice was a reserved velvet murmur: “Are you... hurt? I would like to clarify, John, that I brought you here only because you would not make it back to the island without mine own assistance. You are free to go.”

John felt like the most loathsome of vermin.

After bringing John back to the safest place he knew, apparently Sherlock’s first impulse was to inquire as to _John’s_ well-being. A revelation had been niggling at the back of John’s mind like a loose tooth, an unacknowledged and discomfiting notion waiting to be jostled free. Sherlock cared for him - beyond merely being an interesting experiment. How had he misconceived the depth of Sherlock’s regard?

 _Easy_ , the little voice in John’s mind supplied. _You told yourself that his interest in you was purely a physical fascination - a dangerous whimsy. You buttoned down your desire. Your opinion of his people is ...uncharitable. You find him beautiful, you desire him, and yet you refuse to acknowledge his personhood. You have been considering Sherlock a monster this entire time. A trial to be endured, not a person. Not really. Not if you are honest with yourself, Watson._

His chest felt very tight, and he couldn’t seem to stop swallowing around a dryness in his throat. Sherlock’s expression was even more guarded than usual, and John realized that the undine was doing his best not to aggravate him.

“I’m fine,” John managed at last. He waded through the water, careful not to touch the wound. “Come - come here, let me see.”

Sherlock turned his face away and pretended to ignore him, but after a moment, his tail did uncurl. John carefully scooped up an armful of plumage. John marveled once again at their weight and sheer size of the caudal fins, which seemed to be intact. If Sherlock were to splay them fully open on land, John expected they would look like a woman’s discarded petticoat.

It was the adipose fin that had been bisected. The torn edges bled sluggishly all the way down the length until they met scale. John had no words. 

“It is insignificant. Fin tears are rarely fatal," said Sherlock.

John sucked his lower lip between his teeth and bit. “It looks painful. How does your kind cope with injury? Do you have physicians?”

It was testament to Sherlock’s scientifically-inclined mind that he was interested in discussing cultural differences even as he bled. “For more serious injury, mine own kind may gather a Choir. The power of the Song is amplified in groups. What is a physician?”

“A physician is a doctor, a medical practitioner, a healer. I dreamed of becoming one when I was a boy, but… it wasn’t in the cards.”

As a child, John had opened his first ‘surgery’ in the room that he shared with Harry and his mum. It was here that John ‘treated’ the various scrapes and bruises that his friends acquired after playing buccaneers. He was probably the closest thing to a buccaneer of the lot of them, now.

Sherlock’s hand was resting atop his, and John didn’t remember it alighting there. The merman’s fingers were long and slender. If he had been human, John would have taken him for a violinist. John rotated his wrist so that his palm pressed up against Sherlock’s, fingertips slotting into the webbing between the undine’s fingers like they were made to fit there. He marveled that this same hand that had just wrought such explicit destruction now touched him with such tenderness.

“I’m sorry,” blurted John.

Sherlock’s gaze flicked up to meet his. John pushed his fingertips along the delicate webs between Sherlock’s fingers, simply to experience that texture. He thought about the seal carcass, which was still lying out on the lagoon shoal. “This morning. What I said about the seals, I am sorry for all of it. Most of all, I... I regret calling you a -”

“Monster?” Sherlock supplied. The cool pad of his index finger rested on the fragile vein of John’s wrist.

John winced. “I know now what a true monster looks like, Sherlock. You are not one.”

“And yet, our kind _cannot coexist_.” Sherlock’s voice was brittle with an emotion John had a difficult time parsing. Regret?

“Bollocks to that. Cor, I would have been _fish food_ today if it weren’t for you. That’s twice now you’ve saved my life,” John said, and as he spoke the words aloud he realized it was true. “I can only hope that I will one day return that favor.”

Sherlock’s gaze softened, and John’s belly went molten with reciprocal tenderness. He wasn’t sure what to say, and the undine was disinclined to comment, so they simply regarded each other silently and let their heartbeats resume a normal pace.

“I must confess to being rather out of my depth. Was that a - was that a _mermaid?_ Blimey, it was. Wasn’t it? You said that they would seem like monsters to me.”

A little line appeared at the corner of Sherlock's generous mouth. “No, that was not a female of mine own kind. Females are --”

The undine shifted in the water in order to get comfortable, but in doing so knocked his fin against the rock and flinched. 

“Careful!” John barked. He tightened his hand over Sherlock’s, watching the undine breathe through his nose until the pain passed and feeling a sympathetic stab in his own breast. “You're lucky it didn't bite you clean in half. In all my years, I’ve seen nothing like that before. What was that monster? Are there more of them?”

“Her own name was Olizarat.”

“Oliza _what_? It had a name?”

Sherlock looked calculatingly at John. Whatever he saw in John’s expression seemed to placate him. “All intelligent beings have names.”

Oh, god. That confirmed it - John hadn’t been imagining the intelligence in the leviathan’s abyss-black eyes. He pulled himself up onto the flat rock and spoke over his shoulder:

“Well. Humans have a name for that kind of monster, too. Leviathan, we call it.”

“Leviathan.”

John wrung out his kilt and sat, letting his legs dangle over the edge. “Yes, leviathan. Are there more of them? What was she, then? Olizarats.”

Sherlock lay back tiredly in the shallows, staring out past John at the seascape beyond the lagoon. He did not answer, so John slapped the side of the rock lightly to catch Sherlock's drifting focus. “Listen, I’m serious. What was she?”

“She was a -” oh, and here Sherlock made a complicated trilling sound followed by a definitive click. Thankfully, he deigned to translate. “One Who Is Named, or perhaps _Named One_. It means she was so very ancient that mine own people saw fit to name her.”

 _One Who Is Named_.

John shivered. “Are there many Named Ones in the sea?”

Alarmingly, Sherlock lifted his hand and spread his fingers wide, until the sun shone through the thin lace of webbing connecting them and John could see the faint marbling of blood vessels. Water rolled down Sherlock's long fingers and beaded on his knuckles. He folded his fingers down to his palm one by one, frowning and looking skyward as though his memory was writ on the cave roof. He was counting, and by the time he got to the other hand he paused at the count of seven. 

“Not many,” he said at last, dropping his hand back into the water. “Her own kind never stay long in one place. Besides, John, you should know: I routinely discard memories that are not of use to me. Mine own brother is the one who hoards useless knowledge.”

John made a mental note to ask Mycroft about leviathans, right after he thanked him for coming to his defense. John wondered if Mycroft would have done anything had Sherlock not gotten involved. He doubted it.

The undine, with one notable exception, seemed to keep to their own.

“Why did you kill her?” John stretched his toes out and tapped them on the water’s surface lightly, his reflection warped on the mobile surface. “If she was intelligent.”

Sherlock sounded amused, as though he had not expected such insipidity from John. “She threatened you. I would see her dead.”

And there it was. Clear as day, an admission that John could finally grasp, pin down until he understood. John sat up straight on the rock and spoke slowly and clearly. “Why me?”

“What?”

“Why me, Sherlock.” John gestured to the ragged edge of Sherlock’s fin. A thin trail of blood zigzagged in the crystal-clean water. “You cannot tell me that you do not care for me, for I will not believe you. You have rather shown your hand. So I am asking you... why me? Will the males of your kind have nothing to do with you? OH! Is it because you know I'm -- I'm... attracted to you? Oh, but I imagine that feeds your ego! It is cruel of you to take advantage of a stranded human. Or is it _because_ I am human? I don’t know if I am anything more to you than, than some _experiment -_ !”

John’s impassioned soliloquy was cut short by a thunderous splash. One moment Sherlock was reclining, and the next his palms were planted on either side of John’s seated thighs in order to loom over him on the rock. John’s heart rate skyrocketed, but it was not fear that sang his pulse to speed. Sherlock’s cool breath gusted over his mouth and the tension between them drew taut as a bowstring.

Sherlock oh-so-gently touched his mouth against John’s.

It was the first time he had initiated a kiss.

For a heartbeat, John did not respond. His body was a conflagration and his brain had quite stopped doing its job. Then his faculties returned and he surged into the chaste press of lips, flinging his arms around Sherlock’s neck, and he caught Sherlock’s narrow waist between his thighs where he sat on the edge of the rock. He tangled his fingers in silk-black curls and licked the seam of Sherlock’s plush lips until the merman opened to him and their tongues met. Sherlock had lips softer than anyone John had ever kissed, and despite the obvious inexperience in the gesture it heated John’s blood. _His people don’t kiss. He is doing this purely to please me._

Sherlock's kiss was the ozone crackle of an impending lightning storm. Their kiss turned sloppy in the wake of their taboo desire; John drew back for air and realized he had never loathed the need for oxygen as much as when he was with Sherlock. They rubbed their faces against each other in primitive claim, arms tangled around each other’s bodies and fingers groping into hot flesh. They panted into each other’s mouths, and John’s cock was proud in his kilt.

He ached for wanting.

“Sherlock."

The undine’s hummed acknowledgment pitched upward at the end in a vague approximation of a question.

“Touch me. Touch me now.”

Sherlock’s palm was on his cockstand before John could even finish his demand, delving in the fabric for the prize he sought. His touch was confident and just shy of too firm. John moaned and pressed crescent indents into the skin of Sherlock’s shoulders, letting his forehead fall to rest against the undine’s neck.

“I like this,” purred Sherlock, squeezing gently. “It is mine.”

“It would be a lot less likeable removed from my body,” John huffed out a laugh into Sherlock’s salty-sweet skin.

“You may keep it,” Sherlock provided, eyes twinkling. He slid down in the water in order to nuzzle his face against the thick spear in John’s kilt. His legs were draped over Sherlock’s shoulders in this position. John lifted his hips obligingly so that Sherlock might remove his garment and toss it onto the rocks.

Sherlock pushed his face into the thicket of crisp cinnamon curls at the base of John’s cock and inhaled deeply, gills fluttering with pleasure. John’s cock was long and thick, statistically above average for a human -- although Sherlock would have no basis for comparison, and could probably care less about the appeal of John’s bits as perceived by other humans.

Seeing the flushed length of his cock fitting against the hollow of Sherlock’s cheek was unspeakably thrilling. His femoral artery was inches away from the undine’s pointed teeth. John carded his fingers through Sherlock’s curls, relishing the sight of that dark head between his thighs. He rolled the cartilaginous nub of Sherlock’s webbed ear between thumb and forefinger.

Sherlock rumbled breathily.

“Like that, do you?” John could hear that his own voice was husky and had already dropped an octave with arousal. “I wonder what other parts of you are sensitive.”

Sherlock made a soft whining sound that provoked John to thrust his hips, smearing a streak of pearly fluid across the undine’s cheekbone. He dragged his fingertip carefully over Sherlock’s shuttered gills and they opened beneath his touch.

 _“John…_ yes, you may touch mine own body wherever you like.”

John was rather keen on this invitation, but then Sherlock licked him and all coherent thought vanished. His soft tongue glided slowly from the base of John’s cock to the crown; a decadent, slow motion that suggested Sherlock was really cataloguing the experience. So much so, apparently, that he immediately repeated the action. Again. And again, and now John was pumping up his hips into the satin-warm cradle and inhaling great heaving lungfuls of briny air.

“Oh, oh --! Please, I need… I need..!”

John nudged his cockhead against the seam of Sherlock’s lips, and the undine briefly flashed teeth at him. John knew something was wrong with him, then, he just knew it - because instead of immediately taking his sensitive bits out of the vicinity of that squaline smile, he spread his thighs in helpless invitation.

Sherlock’s eyes softened with something not unlike amusement, and he held John’s thighs where they rested upon his shoulders. He let the head of John’s cock penetrate his lips, very slow and careful of his teeth.

_Hot, wet, good. His skin is cool but he is warm inside. Oh god, he’s never done this before - he has no idea the depravity of the act, he is just intuitively this accepting. Oh sweet Mary, let's hope he doesn't bite down --_

John’s nipples were tight with arousal when he dragged his own nails over the furled peaks, and the sensation was so intense it bordered on painful. Sherlock languidly bobbed his head down and meticulously sucked John’s cock into his throat. John threw his head back and shouted, a brief bark of pleasure that he instinctively bit down.

Sherlock withdrew with an unhurried slurp; clawed fingers cradled John’s bollocks with languid delicacy. “Mmm, no, let me hear you, mine own.”

John growled in acknowledgment. He was marooned on a desert island - how could he forget? He didn’t need to be quiet here, for there was no one within miles who could hear. Instead of provoking a fit of melancholy, John found this idea thrilling.

Sherlock rolled his tongue slickly over the crown of John’s cock, then sunk back down, lips gently stripping back his foreskin. Sherlock kept it all soft and slick, doubly careful for the presence of his sharp teeth. He cupped his tongue along the thick vein striping the underside of John’s cock and suckled in waves of varying pressure.

John suppressed the bestial urge to fuck the tight hug of Sherlock’s throat. That would no doubt result in the amputation of vital parts of his anatomy. He wanted to hold the undine’s beautiful face down, pump into his mouth until he spilt his pleasure down Sherlock’s porcelain throat. John’s bollocks were drawn up tight to his body already.

“S-Sherlock, oh! So good, oh. Quicker, come on now -- !”

The sound of John’s voice spurred Sherlock to a heightened state of lust. He withdrew from what he was doing and surged up onto the rock, hustling John back to make room. His pelvic fins gripped John’s hips hard, a firm press of flesh that tolerated nothing but compliance as a big hand took up where his mouth had been. Sherlock’s shoulder jerked with the rhythmic motion of his pumping hand; his focus so intense that John felt like a butterfly pinned to a board.

“Now,” Sherlock demanded. He laid his forehead against John’s, noses brushing.

John's paroxysm struck like a thunderbolt. He spent in great pulses into the strong cage of Sherlock’s palm and he was acutely aware that he was spending into the same deadly hand that had just ripped open a leviathan’s face in defense of his life. And god, did it feel like absolution. _This is mad, oh, oh, oh!_ The muscles of his abdomen contracted painfully and John curled into Sherlock’s body, shoving his face into the crook of his neck. He was cursing repetitively, the stunned mantra of a new believer.

Sherlock was humming deep and contentedly in his throat.

He laid John down on the flat rock with a supportive arm, ornamenting himself adjacent as John melted into postcoital bliss. His muscles felt like honey, his orgasm the sweetest relief he had ever known. He floated above all earthly concerns. For the moment, the horror of Olizarat was but an echo in the periphery of John’s consciousness.

Sherlock licked the pearly fluid from his fingers with a curious hum, utterly shameless. John’s spent cock twitched optimistically. The undine catalogued the taste with glittering satisfaction, then thrust his nose into John’s neck and inhaled.

John grinned, still panting to catch his breath. “D’you have a keen sense of smell, then?”

“Not at all,” Sherlock admitted, unperturbed at the choice of pillow talk. “Though I believe I am coming to recognize the scent of your own desire. I have observed that scent is more important to humans than it is to mine own people.”

John was was distracted by the bunch and flex of Sherlock’s obliques as the undine arranged his heavier lower half on the rock. He couldn’t wait to experience the difference in texture between scale and skin with his tongue. But Sherlock heard something and sat up suddenly. In a second his energy had transformed from sensual to deadly; John sat up as well and followed Sherlock’s gaze out into the lagoon.

All John could see was a pelican, standing out on the shoal.

“What is it?” John whispered, filled with dread and a bit disorientated from the sudden change in atmosphere. “What do you hear?”

Sherlock did not reply. He shot back into the sea; his wounded tail sent up a swirl of rust and John cried out in sympathy. He scrambled to the edge of the rock, reaching.

“Careful! Sherlock, wait, please!” John cried, distressed.

The undine doubled back and emerged briefly to butt his cheek into John’s outstretched hand. John tightened his fingers in Sherlock’s wet curls.

“John,” rumbled Sherlock. His hand came up and he caressed John’s face with such infinite tenderness that something fragile inside of him cracked, just a little.

“What is it? I don’t speak bloody _undine_ , you have to tell me,” John demanded, resisting the eccentric compulsion to bite Sherlock’s fingers or pull his hair. “Where I come from, it’s a bit rude to toss a bloke off and leave right away.”

“It cannot be helped. Mycroft requests mine own presence. See how he sends a messenger to mine own territory,” Sherlock said, pressing a kiss to John’s palm so naturally that the sailor gasped.

“A messenger?”

Sherlock nodded out into the lagoon, where the late afternoon sun painted the shoals in crisp gold. The seal carcass was a quiet lump on the western shoal. On the eastern shoal, the pelican was... well. Now that John looked closer, the bird  _was_ looking directly at them.

“Something is wrong. He never sends Anthea. I will return --”

“What? No, no. You can’t leave me now, Sherlock, I haven’t even, ” _touched you, and I so desperately wish to, and what happened today was unreal and I don’t want you to go, you’re the only friend I’ve got here._ John’s face flushed. He was suddenly aware of his own nudity. “I want to touch you. I want to know you, Sherlock. You’ve had me twice now and _damnit,_ why are you looking at me like that?”

Sherlock had cocked his head to the side and was considering John through amused seaglass-blue eyes.

“I want nothing more than to feel your hands on mine own body,” Sherlock admitted. He paused. “Will… will you be here when I return?”

That was a loaded question.

John thought about it. He was free to go, if he chose. He knew that Sherlock would not prevent him from leaving this time. Olizarat’s appearance had been a freak incident, like a natural disaster. Although John understood the likelihood of encountering another sea monster twice in one day was slim, he was reticent to plunge back into the deep.

His post-orgasmic lassitude was the nail in the coffin. John needed to rest his exhausted body. He would have a go at swimming to the island after his muscles had returned to some semblance of functionality… and not before he had fully sated his desire to know Sherlock intimately.

“Go on then. I’ll be here.”

Sherlock nibbled John’s fingertip carefully, which surprised a laugh out of him, and departed. John watched as the pelican took flight, circling low over the waves and threading out to the southeast.

~  ~

John did not mean to nap.

He fully intended to occupy himself somehow while awaiting Sherlock’s return. Perhaps he could skin the seal carcass. But he felt like a wrung-out old flannel, and his physical and emotional exhaustion quite caught up with him.

Unfortunately, he dreamt.

John dreamt of his hammock back on the frigate. He dreamt of sex with Sherlock, although he was not a merman at all, but a human being with slender coltish legs and a plush arse. In his dream, human Sherlock was whining and mewling and fucking his hips back onto John’s heavy cock, sobbing John’s name, shivering, destroyed.

And then the scene changed and now John dreamt of the deep water.

He swum in an abyssal trench as infinite as the space between stars, where brine shrimp the size of dust motes hung in the stillness. Jellyfish as clear as cut crystal floated like marine will-o-wisps, their tentacles finer than lace. Sherlock was there. He was undine, now, magnificent in his true form. A part of John breathed a great sigh of relief. Sherlock as a human being registered as _wrong_ in the very marrow of his bones.

In this slumbering fantasy, John was also undine.

And Sherlock was fucking him. They were clutched together, Sherlock’s pelvic fins a punishingly tight vice around John’s hips, a monstrous cock impaled to the root in John’s somehow receptive body. He tried to look, tried to see how they were joined but his dream refused to clarify. Everything was muzzy and indistinct, but the sensation of being filled, plugged, owned, _claimed_ was overwhelming.

Sherlock was whispering to him, not in English but in the strange clicking whistles of his people.

“John, yes. Finally. I’ve dreamed of this for so long, you’re perfect. Be mine. Stay with me, always, mine own. Say that you’re mine.”

John hesitated.

Sherlock slapped his hips forward hard, butting the head of his cock against a new and tender place inside of him. John winced and sunk his nails -- which were claws now -- into Sherlock’s back. It did not occur to him to wonder whether Sherlock actually had a penis, or where his own engine had gone; John’s dreaming mind refused to explain.

“Say it, John,” dream-Sherlock growled, skidding his cheek beseechingly against John's.

John tightened his internal muscles, squeezing Sherlock’s length inside and causing the larger undine to moan, eyelids at half-mast and lips parted as though John were the most marvelous thing he’d ever experienced.

“You already know it,” John heard himself saying, entirely without lucidity.

And then Olizarat came.

The sea monster was not whole. Smaller sharks and fish had eaten the flesh from the leviathan’s bones until she was a swimming skeleton. The torn flesh of her ruined jaw dangled freely as she came upon them, and the darkness of the abyss around them was all-encompassing, the silence as weighty as London fog.

John tried to scream, but no sound came out. He was paralyzed, unable to command his own body. Olizarat’s destroyed jaw was creaking open, the toothy cavern easily large enough to swallow the pair of them whole

and

she

did.

“ _John!”_

He surged awake in a sheen of sweat and terror, and the ivory-handled knife was in his hand and in his disorientation John stabbed.

The knife pierced flesh. The leviathan wasn’t going to get him without a fight. John’s eyes adjusted to the darkness - and, _oh_ , _I am not underwater at all. I am breathing air, cool air, it is night and I am in the grotto. I am whole. It was a nightmare._ Sherlock’s startled grunt of pain incited lucidity.

The undine was near the edge of the flat rock. John released his hold on the knife in horror. He had stabbed it clear through Sherlock’s hand, the metal blade visible on the other side.

“Oh, sweet Mary.”

Sherlock grimaced. This was a new expression, and John refused to look away despite the twist in his heart. His mythological companion was exhaling slowly through gritted teeth, gills clenched so tightly shut that the skin blanched even whiter than usual.

When had Sherlock returned from his rendezvous with Mycroft? How long had he been there, watching John dream?

_I hurt him!_

John reared back on the rock, nearly falling into the water in his haste to put distance between himself and the damage he had unwittingly caused. He was mumbling incoherently, an outpouring of nonsense that sounded like _no_ and _please_ and _Olizarat was here and you were inside me and I didn’t mean it,_ and _I want London_.

Sherlock’s eyes widened with alarm. He floated cautiously around the rock to John, both hands raised in a universal gesture of supplication, but all John could focus on was the knife, sticking out of Sherlock’s palm like a needle drawn halfway through fabric.

Then Sherlock began to softly hum.

John felt the siren call, an overtone droning sound, tug at the corners of his psyche. It rolled over him and into his body in slow, almost erotic pulses. The fear drained from him like poison being sucked from a wound, replaced with soothing certainty: it was all right. No one was going to die. It was only a dark dream, and all creatures lash out when they are afraid. For once, John found himself welcoming that supernatural purr. It sped his comprehension.

“Sherlock. Your hand!” John rasped, jumping into the sea.

He took Sherlock’s pale wrist and stared miserably at the damage. The knife had pierced cleanly all the way through the undine’s pale palm, sliding tidily between delicate bones and the latticework of veins. Deep red blood was oozing from the entry and exit holes.

 _Like Jesus,_ John thought absurdly, utterly off his head. _Ha, it’s positively Christlike._

Sherlock observed him with the careful interest of a scientist whose long-running experiment had just exploded without warning. The Song faded. “You were dreaming. I watched you. At first I thought it was a good dream, but then you began to cry out.”

Sherlock gently extracted his hand from John. He took the handle and tugged; the knife slid wetly free. The merman was stoic, but John winced hard enough to rattle both their bones. Sherlock dipped the knife in the water to clean it, then flicked it dry and handed it back to John, handle-first.

John looked at it. “You’re seriously giving that back to me. After what I just did.”

Sherlock cocked his head to the side. He did not seem to understand. “It is your own. Your puny human body has no natural weapons, John, you need all the help you can get.”

John snorted back an inappropriate laugh. He took the knife and carefully put it back in its sheath.

“This is twice now that you’ve been hurt because of me. When we met your body was unmarred, and now in the space of one day I’ve gone and put you through the wringer! What’s next, then?”

John tried to work himself back up, he really did. He wanted to be more impassioned, wanted to rant his frustration with his own impotence in this world of myth and nightmare, but Sherlock’s siren Song left John pliant. He experienced his regret through a residual soothing veil. The warm water lulled him.

“Any scars acquired in the service of mine own little human are scars I wish to keep,” said Sherlock.

Then he did something extraordinary. He lifted up John’s right hand, the one with the red oyster-shell scar, and laid his bleeding hand palm-to-palm against it. 

“Oh,” John breathed. He could feel the warm tickle of the merman’s blood pooling in their pressed palms. The symbolism was not lost on John. Their wounds had each been caused, indirectly, by the other. Without words, Sherlock communicated solidarity and regret.

Sherlock smiled the tiniest bit and flexed his hand, encouraging John to slot his own fingers into the webbing between his, as they had done before. He could feel Sherlock's pulse thumping wetly and steady as a metronome.

“Olizarat is dead.” Sherlock told him solemnly, and nodded to the rock behind them.

John craned his neck to briefly glance at it, then did a double-take. One of Olizarat’s teeth was there, a huge white awl with a serrated edge. Sherlock must have brought it back with him. The sight of it, so obviously detached from its owner, was more comforting to John than any words. He found himself smiling, albeit shakily.

“You give me too much. If I didn’t know better, I’d almost say you were courting me!” John giggled to palliate this allegation.

But Sherlock replied gravely, “And if I was?”

John was struck dumb. _That would be madness. He can’t be referring to some kind of commitment beyond the carnal touch._

They released their clasped hands and locked gazes instead. Sherlock had very bright, pale eyes with a thick lace of black lashes. His pupil was a perfect inkspot in a disc of sea foam green. But John knew that could change like the tide of the ocean.

“I don’t know _what_ to make of you. It feels like I’ve known you a lifetime, sometimes... There is more to you, I think, than you would have me know.”

Sherlock was hanging onto his every word. After a long moment, he spoke. His voice was low. “I would have you know me, John Watson.”

And John’s heart swooped with a terrible cocktail of elation and apprehension.

**Notes for the Chapter:**

> This was a really fun chapter to write. Teehee.


	11. Surge

**Notes for the Chapter:**

> Monster dick alert, here is your last warning - although the squeamish probably jumped ship ages ago. In related news, Bad Dragon is a really fun website for weird dildos! If you’ve made it this far, you’ve probably been waiting for this. But don't take everything you see at face value, because Sherlock has a few more anatomical surprises up his sleeve…
> 
> Unrelated to dickings: I learned about the [horrifyingly brief life spans](http://www.coltonhistorysociety.org.uk/sickness-Vict.php) for the working class during this time period and winced at the age I had decided to make John (back when this story was still a one-chaptered zygote), but we'll chalk the fact he made it through his twenties up to being a lucky bastard! 
> 
> Here’s a photo of Martin Freeman that looks damn close to [how I imagine John in Riptide Lover](http://jinglebellfic.tumblr.com/post/104028617951/mortinfreemon-oh-god).

The quality of his acquaintanceship with Sherlock changed after that.

Unfortunately, Sherlock was hampered by his wounds. He favored his fin and hand terribly, and this put a damper on further carnal exploration of each other. Although John’s lust was a fire in his belly, he decided to wait until Sherlock stopped flinching when his fin so much as grazed the seabed.

But oh, how he wanted!

It was a trial to restrain himself, sweet torture to observe the undine circling carefully in the lagoon. Even wounded, Sherlock’s body was poetry. The undine was graceful in the way of all truly wild things. He was possessed of an energy akin to a stag in the deep forest. Some times, John wanted to tame him -- whisper soft words into the his ear and gentle his hand down bucking onyx-scaled hips. Other times, John wanted to own Sherlock, ride him to the sea floor like a Spanish horse until he gave in.

And other times still, John simply wanted to be in Sherlock’s presence.

The undine was unpredictable, but John thought he was beginning to understand Sherlock's motivation. Storms were a stimuli on which Sherlock was particularly dependent. Sherlock _loved_ storms. He could predict with enviable accuracy the approach of a tempest. His pupils would dilate to that feral squiggle, and with quivering anticipation he would circle endlessly in the lagoon until at last the skies broke. Then Sherlock would disappear.

John envied the sea on these occasions.

During this week of healing, John experienced no great urge to leave the grotto. It was the safest place to be, and although he did not like to admit it, John craved security. In the wake of Olizarat, John did not wish to weather the challenge of the island alone. 

Confined to gentler currents while his fins healed, Sherlock became violent in his boredom. He killed any bird or beast that was unfortunate enough to alight in the lagoon, and threw the uneaten bodies on the shoals until the smell got so bad that he was inspired to clean up after himself, at which point Sherlock threw himself into the role of marine caretaker. The undine obsessively cleaned his lagoon; digging underwater in the silt and hauling debris out into the open ocean.

“Like a great nesting bird,” John muttered, watching his companion pitch a handful of detritus over the western shoal and out into the sea, where it was caught up by some supernatural undertow and sucked away.

John benefitted from Sherlock’s idée fixe as well. In the sea cave, food and fresh water manifested like clockwork every morning. After a few days of this, John was certain that he had gained a pound, a suspicion the sailor desperately hoped was true. He had become frightfully lean over the course of his stay on the island.

The passage of time was impossible to calculate with precision. By John’s estimation, he had been there for over a month, possibly two. He entertained the idea of tallying off the days by scraping markers into the cave wall, but when Sherlock caught him doing it he snarled and cracked the rock John had been using in his fist.

“Not in mine own nest,” hissed Sherlock furiously, running a palm carefully over the white scratches John had made as though his touch could erase them.

John had tried to get close to him as apology, but Sherlock hissed and flexed his claws until John left him well alone. Thankfully, Sherlock let go of his grudge a few hours later, and came over to rub cheeks with him. John wished that Sherlock was keener on kissing, but it was an activity that just didn’t seem to come naturally to him. He was enthusiastic when John initiated, but otherwise seemed to prefer nuzzling and gentle bites. Sometimes, Sherlock would take John’s fingers in his mouth and close his teeth carefully over them. He wasn’t biting, just … holding him there.

Was it some kind of trust exercise? It seemed to relax Sherlock. John pretended to be put upon when Sherlock did this, but he secretly relished the faint white indents left in his skin.

One brisk afternoon, John sat cross-legged out on the shoal, enjoying the first spot of sunshine in two days. He plaited palm rope around the root of Olizarat’s great tooth. It was an indulgent activity, but John missed the weight of his lucky talisman. He had no idea where Sherlock had hidden the thing, and the undine certainly was not wearing it.

Suddenly, Sherlock hurtled into the lagoon and sent up a great crash of water as he came.

“Dramatic,” deadpanned John, but he was secretly pleased. He wiped sea water from his face with the back of his hand and went back to his project, threading a loop through the bight. If Sherlock was moving that powerfully, he must be on the road to recovery. Sherlock circled in the lagoon twice, a dark blur. John watched this chaotic twirl of energy for a moment, and then decided Sherlock was probably too exhilarant to be civilized today.

“Find anything good in the storm, then? Jewels, ship parts, skeletons? How’s the tail?” _And the hand_ , John could not bring himself to ask aloud.

Sherlock’s face emerged. The sunshine made glossy his dark hair. “Redundantly dead things. Dull. Mine own fluke is mostly healed.” 

To demonstrate, Sherlock displayed his tail fins. It was difficult to ascertain how far along in the healing process the torn fin was.

“I’ll take your word for it. It’s hard to see through the waves.”

“How puny your own human eyes must be.”

John raised an eyebrow. He could convey a magnitude of meaning with the barest of facial expressions, and this he now did. Sherlock smirked, smug in his undine superiority. He drew close, pushing a comber onto the beach with his movement. “What are you doing?”

By way of explanation, John cinched the knot closed around the base of the tooth hung it around his neck, feeling the cool weight of Olizarat’s fang thump against his breastbone. The tooth was very long and heavy. It would make an acceptable weapon in a pinch.

“Clever little hands, John. How long do humans live?” Sherlock's tone of voice was conversational.

John blinked. “Back to the questions now, are we?”

“You promised to answer."

John thought about it. “I once met a bloke who said he was sixty-four. Looked like an old leather bag left out in the sun, he did. The skeleton in your hoard looks livelier!”

“How many years are you?” Sherlock wanted to know.

With a stretch and unperturbed smile, John replied, “Thirty-two.”

Sherlock went very quiet.

“How old are you, then? Do undine live very long?”

Sherlock drew up and partially onto the gravel beach nearby. He folded his arms and lay upon his belly, placing his chin atop his crossed wrists. His gaze fell to Olizarat’s tooth where it hung in the groove between John’s pectorals.

“Those numbers mean years, correct?”

“Of course,” John chuckled.

Belatedly it occurred to him that the undine might not perceive time the same way humans did.

“Mm. I am not sure how many years I have. Many more than thirty-two, though.”

“More than sixty-four?” John asked, reaching out to tuck black curls behind Sherlock’s webbed ear. This coddling was permitted with a haughty sniff, but John knew by now that Sherlock liked it when John touched him of his own accord, and without fear.

“I think so. Mycroft pays more attention to these things than I do. He lords his own years over me at every opportunity.”

John’s cheek twitched in perplexion. “I thought you said that Mycroft was your brother -- your clutchmate. Aren’t you both the same age?”

“Mine own sire did not release our clutch all at once. He birthed half of his own carried clutch first, and in that half was Mycroft. Mine own delivery came several years later... if Mycroft is not exaggerating our age difference,” Sherlock said patiently, as though it made any semblance of sense whatsoever. “How old is your own brother Harriet?”

“Sister,” John reminded him. He knew that Sherlock knew that word, he had heard the undine use it before. “Women brothers are called sisters.”

“Or man sisters are called brothers,” Sherlock replied with a whimsical slap of his tail.

This was a novel statement, and John laughed aloud. Momentarily Sherlock joined him, baritone laughter resonant. John loved the sound.

“What are undine families like, then?”

Sherlock’s laughter faded to a chuckle. He rolled his eyes, a gesture he’d picked up from proximity with John.

“Don’t roll your eyes at me. I get to ask a question now. That’s how this works.”

“It is fair,” Sherlock acquiesced with an indulgent smile. “Mine own kind keep to themselves. The females live different lives. Nomadic, as I have said. Mycroft tells me that most pair-bond with other females in their own pod.”

John was quiet as he processed the idea of marine valkyries terrorizing the ocean in their sorority pods, and marrying other women. After a moment, he decided it was no stranger than meeting a living, breathing merman in the first place. 

“What about... men?” John asked. “What about you?”

“Solitary. Most other sentient creatures infuriate me, John; they are intolerably dull. Some pair-bond with other males and share the nest. _Caring is not an advantage._ ”

This last remark sounded very forced, like something Sherlock had learned by rote.

“So you don’t have families at all, then?”

The undine thought about this for a while. A gull quarked somewhere far above the island and the grotto. Sherlock spoke carefully, “It seems that this concept is more important to humans.”

“Well, certainly. You’ve got Mycroft, haven’t you?”

Sherlock gave John a sharp look out of the corner of his slanted, wide-set eyes. “Mycroft makes a habit of sticking his own giant nose where it doesn’t belong. It has gotten him into trouble his entire life. Take the time he lost his own fin protecting me, for example, and that isn’t the first time. Why, when he was a fingerling he fraternized with humans frequently.”

John leaned forward. “ _Did_ he! I wonder… is that how you learned how to speak English so well?”

Sherlock’s eyes crinkled with pleasure. “Sound deduction. Yes, in part. Mycroft loved humans. Mine own people speak many languages; it is our own gift. _Parli Italiano?_ ”

“Did you just ask me if I speak Italian?”

Sherlock flicked wet black curls back into place. It wasn’t an answer.

John recalled the polite way Mycroft had engaged with him when they had first met. Mycroft’s initial behavior was much more civilized -- well, humanlike _,_  than Sherlock’s had been when he encountered John that first stormy night. It wasn’t a stretch to imagine Mycroft conversing with a star-struck human on some quiet beach.

Honestly, the fact John had survived _Sherlock_ this long was a more difficult concept to grasp.

“Loved humans, you say? Not anymore?”

Sherlock's pale eyes sharpened, but John did not heed the warning in them. He pressed. “You must tell me.”

“I must do nothing!” snapped Sherlock suddenly, and his gills flared out like those Siamese fighting fish.

They scowled at each other.

Then the corner of John’s lip quirked up accidentally, just a little bit, and Sherlock mirrored him, and then they were both chuckling and scowling and trying very hard to keep their eyebrows low and their mouths hard. John capitulated first, dissolving into irritated chuckles. Sherlock followed suit. The tension was gone.

Sherlock pushed himself back slightly into the water in order to submerge his rib gills. He reached out to settle his hand proprietarily on John’s calf, thumbing through the crisp hair there repetitively. “And what of your kind? What do humans do?”

“For families? Well, marriage of course. We get married.”

“What is married?”

“Marriage. To get married, man and wife. United in a marriage,” John repeated, realizing he sounded barmy.

“Yes, marriage. What is that?” Sherlock asked. His gleaming fluke played peek-a-boo just under the surface out in the lagoon.

 _Cor, he’s just enormous_. _I’m never going to get used to it_ , John thought.

He pressed a hole into the fine gravel with the heel of his palm. Bits of shell shone like broken teeth amongst the grit. He watched as the gentle tide gulped over the rim and filled the hole with water. Sherlock’s white-hooked claws carded very gently through the hair on John’s legs, touch so feathery that it tickled. John flexed his toes.

“Well… if a man meets a woman and falls in love, he might propose to her. They agree to share everything, to be together until death do them part.”

"What if the woman proposes to the man?”

John had been anticipating this question, but he had no good answer. “Well, that, er. It isn’t commonly done,” he hedged at last. “It is traditional for the man to ask the woma--”

“Tradition is an idiot,” Sherlock commented, inadvertently slicing down centuries of human mores. “How does he propose this marriage? Will he bring gifts?”

“Yes, sometimes,” John was amused. “It can be quite a lengthy process.”

“How does he know if she agrees? Do they start to dwell together or is it... explicit?” Sherlock closed his enormous hand around the fine bones of John’s ankle. He lifted up his foot in order to examine the underside of it, spreading John’s toes open.

“He proposes, and she tells him yes or no. If she says yes, the engagement is finalized with a symbolic token of their marriage. A ring.”

“Why a ring?”

“It’s traditio-- er, hmm. Well. I'm not sure why a ring. I suppose it could be anything, but they will wear those rings for the rest of their lives, so everyone knows the depth of their regard.”

Well. That was actually a gross simplification, and the bemused glitter in Sherlock’s eyes told John that the undine understood this. He dropped John's foot into the sea with a splash, and the undine's mischief ramped up with his next breathy demand: “Propose to me.”

The command was so absurd that John immediately took up the lark, rolling to his knees in the shallows. _Well, if there were any doubts to my sanity before let them be laid now to rest_ , John thought cheerily. He inhaled deeply, preparing for a theatrical performance. But Sherlock gave him a dark look. “No, do not be silly now. You must do it properly.”

John laughed. Of course Sherlock would want a demonstration to be as accurate as possible. "I shall do what I like! You can't tell me not to be silly. However..."

He genuflected. Sherlock sat up excitedly, thick black tail eeling through the water until he was quite perched upon himself. He stared down at John with rapt expectation.

“The things I do for you,” John chuckled, reaching out to take Sherlock’s unwounded hand in both of his. He looked deeply into Sherlock's eyes, and when he spoke his voice came out much lower than he intended. “So, here I would say to her: will you marry me?”

Sherlock looked down at him, his large hand clasped in John’s smaller, sun-bronzed ones. His seaglass eyes were flicking keenly over John’s face; probably cataloguing the thin line of his mouth, the generous crinkle of amusement at his eyes, and the soft sweep of his short blond hair.

John, absurdly, found himself hoping he passed muster. 

Sherlock’s hand tightened in his. When he spoke, his voice was solemn: “Yes.”

There was a heartbeat’s pause.

Then they both burst into delighted laughter and John rolled into the ocean with unadulterated amusement, feeling the strong bands of Sherlock’s arms catch him immediately and draw him in close. The undine’s hand closed gently around his throat. John’s laughter did not abate in the slightest: Sherlock was obviously trying to experience the vibrations of John’s laughter, not strangle him.

“You goose,” John gazed up at Sherlock’s smug face, curling his fingers loosely around the bony wrist at his throat.

A gull called somewhere far above. It was a pleasant afternoon. Things felt, well, almost normal. How the hell the reserved and prickly Sherlock had gone from trying to drown John on a daily basis to trying to make him laugh was a mystery. He tried not to look a gift horse in the mouth.

“Now, that brings me to another question. Ah, let me go, I want to sit on land,” John grunted, wriggling free and slugging his way onto the shoal.

“Ask.”

“You mentioned a pair-bond. Is that like marriage for your people?”

“I suppose. One may have many sexual partners for the Riptide. It is unimportant; to a human I understand this would seem curious. But a bonded one is one you choose as your own, until the abyss claims you. You share the Riptide, and every resource: food, nest, territory, new lovers.”

John’s throat went dry.

A perverse fantasy manifested in his mind, then: multiple merfolk rubbing sinuously up against one another underwater, hands and lips and flukes stroking in a maelstrom of eroticism. He imagined a bonded pair smiling knowingly at each other while a tertiary lover shuddered with pleasure between them. The undine were so different from humans, who seemed in comparison deeply jealous and petty.

Sherlock’s focus was so intense upon him that John felt flayed alive, every inch of himself exposed to that calculating silver gaze. He got the uncomfortable but titillating sensation that the undine was reading his mind, or at the very least noticing minutiae about him that gave away his thoughts. To prevent him from saying anything scandalous, John circumvented: “It seems to me that merfolk are a very, er, unhindered people.”

“It seems to me that humans willfully shackle themselves to the will of others, and do naught but complain for it. Yours is a people well-suited to subservience.”

This bit rather close to the bone. John scowled. “And you would rule me.”

“I didn’t say that,” but Sherlock’s pupils dilated rapidly into that feral cuttlefish-squiggle, which quite gave him away.

“The idea excites you!” accused John, annoyance and a thrill of something else tightening behind his navel.

Sherlock’s gaze flicked briefly to John’s scarred hand, then back to his face in a searching manner. “You are too willful to be human. You are more suited to life amongst mine own people.”

“Hardly,” John snorted, deadpan and honest. It did not occur to him that this might have been a compliment. “Your people frighten me; it seems to me that every undine lives for himself and cares naught for his fellows. If you were human, you would understand.”

Sherlock's pupils shrunk in alarm. "Ugh! What?"

“If you were human,” John repeated. He pushed aside the niggling suspicion that he had just crossed a line. “I know it’s not possible, of course. I just - well, if I’m honest I did dream it once.”

Sherlock reared up tall, offended beyond measure. In a second the energy of their discourse took a plunge for the dire. “Do you know why mine own people worship no god, John?”

John blinked. He was fairly sure that he hadn’t mentioned the concept of god. “What?”

“It is because I am god. The ocean does as I bid. I do not know the ways of porcelain, of _fork_ and _mustard_ and _silver_. Your own kind fears me, because I remind them of something dark, that they might have dreamt... a secret they do not wish shared.

“The ocean Sings me. It is my blood and my blood is power. Why should I sacrifice mine own strong tail for the chains of the human world? Would I willingly submit myself to captivity by any will not mine own?”

Sherlock unfurled the huge curtain of his gleaming fluke until it was spread behind him, fanned out like the tail of a peacock. The sunlight poured through the semi-transparent skin. It gleamed in a thin gold rim-light on the edges of the undine’s nude body. Despite the vainglorious overreaction that was Sherlock’s little speech, John could not deny the thread of truth in it.

Still he bristled and came to humankind's defense. “Hey now, that’s rude! And sacrilegious, although I suppose that matters naught to you. Humans may not be powerful islands unto ourselves, but collectively we are strong. Different from you, yes, but being a human couldn’t possibly be that bad.”

 _We might not be fierce and free, but there is beauty in our industriousness. I must make him see._ John scrubbed his hand over his face, smoothing his cinnamon-blond whiskers.

“Humans, we create, collaborate, and improvise, and through the years we prevail. If you could only see London, Sherlock! You would understand then. My people, we build like nothing you’ve ever seen. We sail on the oceans, we travel efficiently on land. Why, there’s an underground railway getting larger every year it seems!”

John did not bother to tell Sherlock that part of the reason he took such fierce personal joy in his career as a sailor was because it kept him _out_ of London. He wanted to impress the undine. He wanted Sherlock to find his kind worthwhile. Sherlock dropped his fluke. His eyes had gone molten as John's passionate response came to an end, and something he said must have worked, because Sherlock's next inquiry emerged non-confrontationally. “ _Railways_ , you say. _London_ , you say. Is that where you dwell?”

“It’s a city.”

“Obviously!”

“I wasn't finished. It’s a complex place. Crowded, teeming with people all going about their daily lives. It’s a bit dirty, the fog always gets worse around noon. You’d think the sun would chase the fog, Sherlock, but it doesn’t. Ah, what am I saying? You don’t want to hear of fog.”

The pea-soupers of London were a dark and cloying thing. Sulphuric and thick, keeping white clothing pure of smog stains was a Promethean exercise in futility. But homesickness lent romanticism to John’s memory.

“Well anyway, there’s Big Ben and the railways, as I said.” John quite fancied the underground railways. “Lots of activity on the Thames - that’s a river, mind, and… damn, what is it?”

Sherlock was sitting up, and his pupils were dilated. He looked enchanted.

“Big Ben _,”_ he echoed reverently, “What is Big Ben?”

John grinned. It looked like he had somehow hooked Sherlock’s interest. Perhaps it was time to share some of the stories he had collected from his extensive wanderings around London.

“Well, you see. It all started with a great fire that destroyed the old palace of Westminster, in 1834 -- that’s when I was born, you know. Off to a lucky start, I was.”

~  ~

By the time the sun set, John’s throat was hoarse, and his arse was numb from sitting.

Sherlock had been riveted by the story of London. In particular, the undine expressed a rather macabre fascination with criminals and the human tendency toward deception. During the course of their conversation, Sherlock acquired more obscure vocabulary -- including ‘biscuit’, ‘handspike’, ‘fuck’, and ‘tea’, not to mention a plethora of nautical terms.

He seemed to comprehend verb tenses intuitively, and picked up new words with a awe-inspiring speed. Although his conclusions were occasionally unethical, Sherlock put pieces together more quickly than any human John had ever met. Despite having a leg up on the merman educationally, John began to feel a little intellectually usurped. He wished he had books with him there on the island that he might be able to answer Sherlock’s desperately sincere queries. There had been a Bible in Sherlock’s hoard back on the islet of Algernon Portnay Kirk. Could Sherlock pick up reading skills with the same unholy speed he did language? Perhaps the undine could acquire more literature in the future; who knew what a shipwreck would leave behind?

When John’s voice cracked for the fourth time in a row, Sherlock held up a hand to stop him. It was obvious he wanted to keep going. There would be other opportunities to discuss their different worlds, and yes, John _had_ promised to answer all of Sherlock’s questions and _no_ he had not forgotten, ta very much and would Sherlock please bring him dinner, he was getting a bit peckish.

Sated and sleepy, John nested himself on the uncomfortable rock.

The Fusiliers’ uniform was a negligible barrier between the hard surface and his protesting muscles, but it was better than nothing. _Fronds!_ John thought to himself. _I’m going to bully Sherlock into getting me some bloody palm fronds, this rock just won’t do. The ugly tree was cold, and this rock is hard. Why can’t a man have both softness AND warmth?_

There was an artificial click, metal, not undine vocal chords. John opened his eyes to witness Sherlock sifting through the pile of treasures they'd brought back from the islet: the mirror, the golden plate and cutlery (currently displaying the detritus of John’s most recent meal), and the compass. But it was not these smaller items that drew Sherlock’s attention.

He had popped open the latch on the violin case. _Does he even know what that is? He will want to know about fiddling, and I play only the pennywhistle._

Sherlock’s velvet baritone filled the grotto without even turning around. “Sleep, John.”

John fruitlessly fluffed the clothes he was bedded upon, in the same idle manner a dog circles its bed before he sleeps. “What do you do during the storms?”

The moonlight shone on the wet curve of Sherlock’s shoulder blade as he lifted the violin carefully out of its case, tilting the instrument toward the light and squinting along its length. “I swim, and I Sing, and I look for disaster.”

“What if there is no disaster to be found?” yawned John.

“Then I create it.”

Well.

John didn’t really know what to say to that. He fell asleep with the weight of Sherlock’s presence stifling in the air around him.

~  ~ 

The sun rose high the next morning and promised a true scorcher.

Although the puncture in Sherlock’s hand was still healing, the undine’s fins were restored in a matter of days. It made sense that a part of the body necessary for locomotion would heal so quickly, John supposed. The merman’s adipose fin was now bisected into two long white streamers instead of a single flag. If anything it made Sherlock’s plumage more fanciful, for the newly-sectioned fin was ribbonlike.

Sherlock drifted up to the side of the rock, belly-up. The majority of his body was underwater, but he arched his spine so that the planes of his abdomen emerged slightly, a flat porcelain island. John smiled. He prodded Sherlock's belly with his foot.

Sherlock did not disappear at the touch, so John nudged him again -- this time skating his toes over the place where fine black scales faded into flesh. The thin skin of the intercostal muscles between Sherlock’s ribs fluttered almost undetectably with his pulse. John leaned out and replaced his foot with his hand, stroking the undine’s exposed belly. Sherlock bobbed compliantly under his touch.

John felt a little thrill of excitement at this docility.

Sherlock undulated his hips up in order to push his wet skin more firmly into John's hand, and rose his face out of the water in order to look up at John. A lock of dark hair swept damply over his cheek.

“John,” he sighed.

“Mm.” John hummed a wordless acknowledgment, afraid to break the spell of the moment.

He continued to caress Sherlock's belly. Clearly it was doing something for the undine. Sherlock's lips parted and his eyes fell to half-mast; the muscles of his torso rolled and flexed handsomely as John firmly pet the skin of Sherlock's lower abdomen and --

Oh, oh Christ _._

Spearing out from between Sherlock's spread pelvic fins was his penis. And John's first impression was not one of disgust, as it probably ought to have been, but instead was a cocktail of arousal and fascination -- a response Sherlock was singularly capable of provoking in him.

Sherlock's cock was not very humanlike.

Not at all.

It emerged from a pink-lined vent in onyx scales. Sherlock’s cock was coral-colored, the only spot of vibrancy on an otherwise monochromatic mythological creature, and possessed of a strong s-shaped curve. It was intimidatingly large: as thick as John’s wrist at the base, circumference gradually attenuating to a fluted and inhuman crown. Ringing the base were a number of soft, fleshy protuberances - barbs, John’s mind supplied with no small measure of surprise, that pointed backward toward Sherlock’s body. They did not look painful to John's eye, which was probably showed how far he had fallen in depravity.

The whole affair glistened with slick, a tempting display of virility. If there were any doubts left as to his undine companion’s sex they were forthwith banished.

“Oh. _Hello,_ ” croaked John.

“Hello,” Sherlock replied. He was smiling faintly, evidently confident in the seductive appeal of what he was displaying.

He rocked his hips up at John in blatant invitation, sending waves sloshing up over the edge of the flat rock. Dappled sunlight from the hole in the grotto ceiling gleamed on Sherlock’s scale-ornamented forehead. Those vivid, wide-set eyes glittered with such deep comprehension that John often had to look away, finding the intensity of Sherlock’s stare quite overwhelming.  _You've practically got his_ _cock in your hand and it's his eyes that make you blush, Watson. Ludicrous._

Although he had no idea what an undine might find sexually stimulating, John was not a shy man; his hand drifted lower and Sherlock did not rip it off. Thinking this was a good sign, John skated his palm carefully over Sherlock's cock. It was blood-hot and throbbing to the touch, slick with natural lubrication. Sherlock sucked his lower lip between his pointed teeth.

“Convenient,” John murmured.

Sherlock showed remarkable self-restraint, lying back in the water and only oscillating his tail slightly in order to stay easily-accessible at the surface. His hands circulated slowly through the water at his sides, not necessary for flotation but dancer-like and lovely to behold.

“What are these for?” John breathed softly, petting his fingertips into the ring of small fleshy spines at the base of Sherlock's cock. To his surprise, they seemed to welcome his touch, flexing around his fingers with slippery pressure.

“Fun,” replied Sherlock. His voice was full of promise and mischief.

John chuckled breathlessly. 

“Also to stimulate ovulation in females,” Sherlock added as an afterthought, gasping when John’s callused palms ghosted down his hips and onto the long column of his tail.

That otherworldly tail. It was the number one defining feature that separated Sherlock from humans... admittedly amongst a plethora of other biological discrepancies. John let his nails catch in the divots between scales, sliding them into the hair-thin seams and pressing a little. The biggest scales were the size of oyster shells, their scalloped edges rimmed with metallic copper. The lamella were tightly interlaced, and he could feel the firm muscle just below.

“Blimey, but you’re a big beast,” John murmured, and then uttered aloud a thought he had rather intended to keep private: “You could crush the life out of me.”

Sherlock didn’t seem put off at being referred to as a big beast, noticing instead the second part of John’s remark. “Does that notion arouse you?”

John’s cock had thickened with interest, but he said nothing. John could feel Sherlock’s pulse under the flat of his palm, where it rested on that hot engine.

“I see. What do you imagine when you take yourself in hand at night, I wonder? Do you envision faceless humans, with hard cocks and soft entrance? Do you close your eyes, John, and remember the feeling of mine own lips? Or do you wonder what it would be like to receive me? Shall I tell you what I imagine..?”

“Don’t --” John croaked, but Sherlock’s big hand covered his and he began to gently move John’s hand up and down his penis, forcing John to stroke him.

“I imagine your legs around mine own hips. Tight, I can feel them, feel your peculiar little feet-fingers kneading into mine own fluke. I want to suck them. I love how they move when you walk, pressing into the earth, never still. I imagine your own body receiving me..." Sherlock’s baritone choked off here with a guttural purr that came from somewhere in his chest.

John was hard as steel and trembling, panting slightly just from hearing those words. He reclaimed his autonomy, letting his hand glide easily over the naturally-lubricated skin of Sherlock's heavy cock. It was so hot to touch, especially compared to the rest of the undine.

Sherlock emitted a quavering groan; John’s attention was drawn to the undine’s throat. He touched the ruffled edge of Sherlock’s neck gills. They folded closed automatically and Sherlock grunted in surprise, eyes flicking to John’s face. John traced his callused fingertips along that invisible seam.

"Tell me to stop and I will," John murmured.

The undine’s jaw slackened and he made a little weak noise. Encouraged, John caressed Sherlock’s ribs, where the powerhouses of his respiratory anatomy resided. “Mmm, could it be you enjoy it when I do this..?”

John slipped his fingertips carefully along a slick pink slit and Sherlock shuddered. His gill was as warm and slippery as a woman’s sex. Perhaps that was what inspired John next: he leaned down, hand still working Sherlock’s cockstand, and licked along the edge of that deep groove. His tongue parted the delicate skin, sliding shallowly into tender flesh. Here Sherlock tasted spicy-sweet and vaguely of anise. Peculiar.

“ _John_ \--!” Sherlock flung his hands out to steady himself. He managed to sound both vaguely scandalized and delighted at the same time.

John sealed his lips around the lacy ruffle of skin and suckled lightly. The noise that Sherlock produced in response was opulent, and spurred John to repeat his attentions on the other side. Foreseeing a crick in his neck, John released the skin between his lips and slipped into the water. Sherlock keened at the loss of contact.

“Shh, none of that. I’m right here,” murmured John, stepping out of his tattered kilt and swinging a leg over.

He climbed up to straddle Sherlock’s hips and they sunk a little under their combined weight. His legs were submerged on either side of Sherlock, but the undine had no difficulties keeping them afloat. The steady motion of the his body brought to mind the swell and ebb of a ship, and that was a location with which John was familiar.

There was so much restrained power in Sherlock’s every movement, shuddering between John's thighs.

It was a dangerous euphoria.

John bent over and stroked his lips against Sherlock’s generous mouth. Sherlock opened to him, the blood-hot velvet of his tongue curling flirtatiously against John’s. The kiss broke when John seized the Sherlock’s cock in both hands and Sherlock jolted. _In for a penny, in for a pound,_ John thought. He rubbed his palms up Sherlock’s cockstand, strumming his fingers across the agglomeration of soft barbs and smiling despite himself when they contracted.

Sherlock bucked blissfully. John tightened his legs in order to keep his seat.

“Sit still!” commanded John firmly, the same voice he used to incite obedience in his peers on board the ship.

Sherlock tried to comply, but he couldn’t seem to stop running his unwounded hand down John’s arm and thigh - too busy keeping them afloat to take John’s cock in hand as he so obviously longed to. John’s body was aflame, every nerve ending was electrical and pointing toward Sherlock. He was so hard it hurt.

Then he had a brilliant idea.

John hesitated for just the slightest moment before pressing down a little on his own penis, brushing it against Sherlock’s. Their cocks touched and both man and merman hissed simultaneously.

“Warm,” purred Sherlock at the same time as John sighed, “Wet.”

Sherlock was breathing open-mouthed, craning his neck in order to stare at the place where they touched. John’s ruddy human cock was slotted up against the subtle, rather more flexible, s-curve of Sherlock’s. Sherlock made a low keening noise in the back of his throat.

“Yeah,” John breathlessly agreed.

John tightened his thighs around Sherlock’s gently pumping hips and held himself steady. This was a job for two hands. Sherlock's cockstand was hot and pleasantly textured; John manipulated himself so that he could nudge the crown of his cock repetitively into the silky embrace of those unusual barbs, and once he got his rhythm he rutted shamelessly, enjoying the slightly awed expression that stole over Sherlock's features as he was ridden hard.

“J-John, oh..!” After a moment he frisked John’s hands away and replaced them with his own, which was large enough to encompass both of their girth at once. The pair sunk slightly and if hadn’t felt so good John might have laughed aloud at the absurdity of the rhythmic splashing that now filled the grotto.

It started as a welling of pressure tugging just behind his navel. It was followed by a tingling in his bollocks, a sensation that radiated up the column of John’s spine like the tide sucking back from the shore moments before a great wave.

“Ah, ah - Sherlock! Hnn, _beauty_. I - I’m -”

Then John was shouting out loud in paroxysm. Lightning bolts rocketed through his frame -- acute ribbons of sensation that manifested as deeply pleasurable contractions; John felt as though he had been holding a part of himself in reserve for hours and was at last permitted to release it. John spent his pleasure in hot bursts over the adamantine curve of Sherlock’s penis.

For a moment, the world came into razor focus. Sherlock was rumbling in approval, an overtone hum that flirted at the edges of a supernatural Song.

John heard Sherlock’s panting as though the undine’s mouth was at his ear, heard the wind whistling outside the grotto, clear and high as a pennywhistle. The scent of the sea cloyed his nostrils; ancient infinity and primal salt. John tasted copper. Had he nicked himself on Sherlock’s teeth again? John’s orgasm resolved like a puppet’s snipped string and he collapsed in slow motion atop his undine lover.

Sherlock swept his hand through John’s pearly spend, smearing it generously along his length. He released John’s over-sensitive cock from the cradle of his fist and took himself in hand. John rested his forehead in the dip of Sherlock’s clavicle; from this acute angle his view of Sherlock pleasuring himself was almost first-person.

“Sherlock, god, yes, I can feel you,” John’s voice sounded destroyed even to his own ears, and Sherlock moaned.

The ocean lapped over them, a sloshing constant that John had become so accustomed to that he barely registered the wet as unusual. He could feel Sherlock’s heart, a war drum, beneath his sternum. _I bet I know what will push you over the edge, you great beauty_. John palmed the undine’s rib gills. The pink slits flexed open whoreishly and John rubbed them with ghostly pressure; at the same time, he kneaded his toes firmly into the dorsal side of Sherlock’s tail.

Sherlock spent; the register of his satisfied moan was so deep that John felt the vibrations hum up through his body.

In paroxysm, Sherlock displayed a curious vulnerability. His great tail breached and then slashed back into the water with a thunderous splash. John gasped and clung on for dear life, more to spare the indignity of pitching sideways into the shallow water than for any genuine fear of submersion. He needn't have worried: Sherlock gripped John’s hips hard, talons puncturing skin and his eyelids fluttered even as he stared resolutely into John's eyes, utterly shameless in his pleasure.

John felt the first spurt of Sherlock’s spend when it struck his belly. It came as a thick, hot pulse, and that in and of itself was not unfamiliar to him, but he had not been expecting the volume; spurt after spurt of hot spunk struck John's chin, dripping down his throat and painting his belly white where he bestrode Sherlock until it flowed in a plenteous cascade down John’s cock and was carried away by the wavelets.

“Gorgeous,” John murmured, rubbing his whiskers against the blade of Sherlock’s cheekbone. He cupped the back of Sherlock’s skull with a hand under the water. “You’re so bloody gorgeous.”

Sherlock might have preened if he weren’t still making a catastrophic mess between their bellies. John shifted, for his legs were beginning to fall asleep and his bollocks were sliding in a combination of sea and spunk. Sherlock tightened his talons warningly on his hips when John tried to dismount and John sighed. He kissed Sherlock’s lips once, twice, thrice, until that generous mouth curved into a smile.

“All right?”

Sherlock’s voice was soft and sex-slurred. “Mmm, yesss. Mine own little human.”

John chuckled. Sherlock sounded drunk, and the sailor couldn’t help but notice that the undine’s ability to tread water had gone clumsy and weak. John, for his part, was more aroused than he had ever been in his life. He felt sated, yes, but his body had been enlightened and cried out now for more of this lightning mix of danger and pleasure.

Sherlock’s eyes were closed and his gills were flared out, petting John's back slowly and obsessively, smoothing his palms down to hold the curves of his arse and squeeze. Then he repeated the gesture in reverse.

“So. Legs?” John said.

He spread his toes and stroked them demonstratively up and down the dorsal side of Sherlock’s tail. The undine grunted irritably. John’s cheeks tightened as his smile grew. _Is he ticklish now?_ The gleam of pointed teeth behind those pretty lips dulled John’s desire to test that theory. _Maybe some other time_.  _Looks like he's thinking about biting me._

John shifted a little to allow the current to flow between their bellies. The ocean made for easy clean up. He ignored the ominous overtone rumble of disapproval; the spoiled prat thought he was trying to climb off again... Then John realized that the hum had been going on for a while, but so soft John could barely hear it. It was like the purr of a cat, but fainter. It had a thoroughly ethereal quality, quiet as it was, and John put his ear to Sherlock’s chest where it was loudest.

“Are you Singing to me?” John whispered.

In response, the hum increased in volume. A blip of nonverbal assent.

“I don’t feel manipulated,” John remarked, folding his thickly-muscled forearms over Sherlock’s narrow breastbone and resting his chin in the divet of his own wrists. He was aware that he was uncommonly talkative, but he couldn’t seem to stop. “Is that a happy noise, hmm? Is that what that is?”

Sherlock groaned and tightened his grip around John’s waist with his pelvic fins. Then he rolled suddenly in the water, dunking a squawking John. Obviously Sherlock was trying to get him to shut up. They play-grappled.

Sherlock was a bit sex-drunk, and John had the advantage of him for once; getting the undine into a chinlock was easier than it had any right to be. _Come on, wrestle back! You’re not even trying._ He felt the undine’s gills fluttering.

_Oh._

Sherlock was laughing.

This realization sent a flood of something warm rushing up from John’s toes. He faux-punched Sherlock lightly in the arm and then made a show of releasing him, standing up and smoothing the water out of his hair. Immediately Sherlock coiled around John’s hips and legs, cocooning him in a funnel of gleaming white fins and inkspill scales.

“That’ll show you to interrupt me,” John panted, snickering. His muscles felt loose and pliable; his brain saturated with a pleasant fog of postcoital hormones.

Sherlock nuzzled his nose into John’s pubic bone, a hot tongue coming out to briefly stroke John’s cock. John inhaled sharply. His cock was half hard. John had thought that level of randiness had been banished to the days before he was shot. He looked down at where Sherlock’s inkcloud of hair swayed in the water below, the strong delineation of muscle of his porcelain back before it melted into the mythological bits of his anatomy.

A muted click rose up from below.

“Yeah,” whispered John, heart galloping with anticipation. “Yeah, all right. Let’s.”

~  ~

The second time had been just as exhilarating as the first: Sherlock had ended up fucking the channel of John’s clenched thighs, John’s hand a blur on his own cockstand. Now they floated together, easy on the water and bonelessly relaxed in each other’s arms.

Sherlock was Singing under his breath again. This postcoital concert seemed to be out of the undine’s conscious control, and John found it too endearing to tease him about it.

“I’m going back out to the island tomorrow,” John told him. He bit the nubby cartilage of Sherlock’s ear, warning him not to disagree.

Sherlock grunted, twisting his face away from the pinching pressure (although the subtle Singing did not falter, and therefore he was probably not as put off as he pretended to be). “Do not try to swim it on your own again, mine own. I will take you where you wish to go.”

John, who had been half-heartedly pursuing the escaping ear fin, drew back to focus on Sherlock’s eyes. “Really?”

“Yes.”

John should have stopped the conversation there, and taken Sherlock at face value. Instead, he found himself speaking and simultaneously thinking he should shut his mouth. “You’re not… I mean, just like that? You’ve been trying to get me back in your nest this whole time, and now you’re agreeing to help me get back to the island. What changed?”

Sherlock deigned to slant open his eyes. “Mine own understanding of... you. Your own stubborn will. You, striking out into the deep ocean alone. In case it had escaped your notice, John, you are lacking in fins -”

“Can still swim,” John interjected exasperatedly. _Why do these bloody merfolk act like I can’t swim just because I’ve got legs?_

“- and I did warn you that there are unfathomable dangers in the ocean,” Sherlock glided over John’s interruption. “It is obvious that you will not stay where I put you. The logical solution is to escort you.”

John felt a surge of gratitude at this. Dimly he was aware that this was hardly a victory; John’s prison walls had merely been expanded to include the island. He almost said thank you, but residual pride reared up and saved him from debasement.

“Ah. Well. That’s… that’s good, Sherlock.”

And since he felt like doing so, John kissed Sherlock full on the mouth.

**Notes for the Chapter:**

> A laborious but fun chapter to write. Here is the silly [playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I listen to when I write, the [bloggum](http://jinglebellfic.tumblr.com/tagged/riptide-lover), and please check the blog for update information as I can no longer answer questions pertaining to that. Comments are the fish flakes in my tank.


	12. The Listener

**Notes for the Chapter:**

> Merry Christmas! For those of you who haven't seen it on the blog I did a quick painting of [undine Sherlock's face](http://jinglebellfic.tumblr.com/post/105500350326/sooooo-i-might-have-just-drawn-a-pretend-cover-for), because this fic is eating my life. (I used it to decorate Chapter 1.) In other news, I wrote the words "scaly derriere" and I feel kind of like I unlocked a major life achievement in doing so. 
> 
> Thanks to my betas JP, Red, and Dee <3

A pale pink sea bream circled peacefully in the island shallows. It was a slim, spindle-shaped fish with iridescent scales. Its mouth opened and closed in a circuitous series of yawns as it combed the seabed, stirring up delicate trails of silt. The gulls quarked overhead, the waves lapped quietly, and the sun was hot in the sky. ****

A javelin thudded into the fish’s body and pinned it to the sugar-white sand, interrupting the tranquility with a splash. Its death throes jiggled the weapon where it protruded above the waterline.

John Watson stood in the shallows off the coast, squinting into the white-hot sunlight. He was back on the island, now, with Sherlock’s blessing. His undine companion had ferried him back two days ago and watched bemusedly as John flung himself into an industrious frenzy, trying to make up for the week that had been lost to their encounter with Olizarat.

He did not know it, but he cut quite a savage picture.

Two months on the island had transformed his body, already strong from a lifetime in the British navy, to something dangerous. The barest skim of extra fat that had once lent softness to John’s musculature had vanished, leaving him granite-hard. His once fair English complexion had bronzed from the relentless sun, and he wore nothing but a tattered kilt. The knife hung at his hip, a second javelin ready in hand.

The leviathan’s tooth was a blinding needle of white where it hung against his chest.

John waded over to his catch and tugged the javelin out of the sand, releasing a cloud of fish blood and silt. He held his speared dinner aloft and the sun glinted off the bream’s scales. John’s mouth watered. He was going to cook this one right away. He already had a fire going with crabs baking slowly in the ashy coals.

 _While I wait for this beauty to cook, I’ll take care of the beard,_ John thought. Rather than lengthening as some men's did, John's beard seemed only to thicken. He had discovered how to keep it short using his steady hands, the blade of the knife, and the hand mirror. It was a laborious exercise in vanity that John maintained primarily as a nod to the increasingly delusional hope that he would somehow be discovered.

A splash nearby startled John. He searched the water with a smile already on his lips. Over the past two days, Sherlock had only shown his face at sporadic intervals - presumably to check and see that John hadn’t escaped. Terrible screeching noises had been sounding with some regularity from the distant grotto.

John suspected that Sherlock was fussing with the fiddle. He would have been happy to discuss instruments and music with the undine, had Sherlock broached the topic, but he was being secretive. If Sherlock wanted to talk about the violin, he would bring it up of his own accord.

John personally doubted that the undine would ever succeed in coaxing anything more than an unholy shriek from the old violin, but he knew better than to give an unsolicited opinion.

John looked out onto the still waters. He could not see anything. Perhaps Sherlock was sneaking up on him again - an unwise decision when John wielded a sharpened stave. Grinning, John sunk into a crouch and did another pass over the ocean, wishing the sun weren’t so brutal. _There!_

As soon as John saw the telltale ripple of movement beneath the waves, a merman emerged - the wrong one. It was Mycroft. Immediately John’s body flooded with adrenaline. The undine were _dangerous_ , full stop, and Mycroft was unfamiliar to him. He was unwilling to turn his back on Sherlock’s elder brother, so he instead held up the bare javelin.

“What are you doing here?” he growled.

He hadn’t meant for it to come out so abruptly, but anxiety prickled the hairs of his scalp. Unconcerned by this brusqueness, Mycroft looked serene as always, head and shoulders above water. The inhuman rest of him was quite submerged (although John could see the bladed tip of a dorsal spine peeking out of the waves behind him).

“John. I promise I will not harm you, or abscond with you this day.”

“Well, thank god for small miracles,” quipped John. He let his javelin point down. “Thank you for the help with the leviatha- er, Olizarat. Is your arm all right?”

“It will heal with time. You are lucky to have survived. Sherlock, too. Alone, I do not know that he would have been able to subdue her.”

Mycroft did not say _you’re welcome_ or offer any human platitudes. The incident with Olizarat had been troublesome for them all.

“I suppose Sherlock called you?” John asked, wondering about the apparent serendipity of Mycroft’s appearance during the incident.

“No. Mine own brother is prideful. I have never known him to request assistance. I heard you cry out, same as Sherlock did. I only regret not arriving sooner... but I am afraid _finwork_ has never been my specialty.”

John said, “Wait. You came because you heard _me_ call for help?”

Mycroft’s pale hand emerged from the water in order to smooth his short auburn hair back. Despite the decorative spray of copper-colored scales on his cheeks and forehead, he really was an exceptionally bland-faced individual, John thought without vitriol. The widow’s peak made him seem more like a real person, or some lost Londoner.

Here John’s imagination ran away with him, and he briefly envisioned the undine as a stodgy vicar. This thought was so amusing that John had to stifle a snort.

“Mine own brother is fickle. And evidently quite attached to you. I came because I anticipated that Sherlock might have needed my assistance. As usual, I was correct.”

John did not know what to say, so he remained silent.

“No,” Mycroft allowed. “It would be best, John, if you assumed that mine own benevolence extends only to Sherlock. Tell me, do you plan to continue your association with him?”

“I could be wrong,” snarled John, suffering from conversational whiplash, “but I think that’s none of your business!”

Replied Mycroft, “It could be.”

“It really _couldn’t!_ ” cried John. “In case you’ve forgotten, _Sherlock kidnapped me_. He’s the one who put me here, he’s the one who is doing the, the _associating_. I can’t even leave this bloody island! And what did you send your pelican messenger for? What emergency prompted that?”

Mycroft’s pupils, which had been bland and humanlike, cinched into a cuttlefish squiggle. This reminded John who - or _what_ \- he was talking with.

“It is business that does not concern you. John! There is a modest human settlement on the mainland northwest of here, several days as the fish swims. I’d be happy to take you there.”

John’s jaw clicked shut.

_A human settlement. Northwest._

“That said,” Mycroft droned on, “Transporting you to the human settlement requires a great deal of time on my part. I should like to bargain with you.”

“Of course you would,” spat John.

Mycroft continued, unruffled, “At first I thought your own presence would be harmless, but now I have come to understand that your human weakness puts Sherlock in a position of vulnerability, and will continue to do so for as long as you associate. You must promise to discontinue your relationship with him.”

 _Associate._ John hated that word, he hated how Mycroft said it soft and sibilant. He was still processing the fact that _humans_ , real other living humans, were not unattainably far away - if one had fins, or some kind of sailing vessel.

“Where exactly is this human settlement?” John inquired, too casually.

Mycroft tutted. “Your motive is transparent to me. That is not information I will divulge.”

Well.

It had been worth a try.

John recalled the dinghy on the islet of bone and felt a pull behind his navel. It might be possible. It was a hellish swim to get to the islet of Algernon Portnay Kirk, but he could do it. Despite knowing now what lurked in the deep water, John was willing to take his chances if it meant his freedom. He didn’t want to put his life in Mycroft’s webbed hands.

Mycroft rose up slightly. His red-and-white striped fluke slashed briefly above the waves, flat fingerlike fins quite dissimilar to Sherlock’s gentle ruffled fan.

“John?” he prompted.

John didn’t like the little half-smirk playing about Mycroft’s lips. The offer was tempting, but John didn’t trust Mycroft, and he didn’t like this particular undine meddling in his affairs. Something about the offer just was not on. He remembered Sherlock telling him that his brother did nothing without an ulterior motive, and although Mycroft had stated the terms of his proposal clearly, John got the feeling there was something that Mycroft was not telling him.

He decided to trust his gut. Better the devil that he knew.

“Well. No. Thank you, but no.”

Mycroft stared. “No?”

“Yes, _no_.”

“Yes or no?”

“ _NO!”_ shouted John.

Mycroft drifted a bit closer. It was evident that he was unwilling to pull into the true shallows, where his enormous tail would cross the line from magnificent to absurd.

“But why in sea not? When we first met, you asked for mine own help; now I offer it to you -”

“At the expense of my association with Sherlock. He said you do nothing without a hidden motive, and I begin to suspect he was right. Good day, sir!”

And here John turned and began to slog through the shallows toward shore.

Mycroft’s voice, when it came, was measured. “John, please. I did not mean to offend. Sherlock is the only one of mine own brothers that I affiliate with. Do you know why that is?”

John’s pace slowed.

Mycroft continued. “Sherlock is a veritable genius. If he cared for such things, he could influence the future of the undine.”

“Undine,” echoed John automatically, copying Mycroft’s pronunciation. _Uhn - deen_. Where had that word come from? It sounded like a human word to John. “You know, my people, Englishmen - we call yours _merfolk_.”

Mycroft’s smile was a vestigial thing. “Mermaids and mermen, yes, I know this.”

John stopped. He hesitated, then decided to forge ahead, though he had already made up his mind. If Mycroft thought there was something to be gained in sharing information with John, he would be more inclined to answer questions and John wasn't above a little manipulation to fill in the gaps of his knowledge about his aquatic companion.  _Captor_ , John corrected himself.  _Sherlock is your captor, Watson, not your companion._

“Mycroft. Where did the undine come from?”

Mycroft hesitated, cocking his head to the side in thought. “It is not known. Where do humans come from?”

John also hesitated.

He thought about Adam and Eve. If he were in London, speaking to a human, he would have recited a verse from Genesis. But there was no civilization here, and John’s darkest suspicions that the Bible was naught but fabrication would provoke no odd looks.

“I don’t know,” he replied at last. “There’s the story of Genesis, I suppose.”

Mycroft smiled faintly. “Mine own people do have a story, passed down through the generations.”

John was both desperately curious and lacking for entertainment, and so despite his distrust of Mycroft he said, “I should like to hear it.”

“As you like.” Mycroft inhaled deeply and settled something in the set of his shoulders; John stood more comfortably in preparation for a tale.  

**The Legend of Undine**

“Once upon a time, many years ago, lived a human lord and lady. Their servant was a woman by the name of Undine, and she accompanied them on a journey by sea. Now Undine and her lord had known each other in the way that lovers do, and Undine became gravid.”

Mycroft’s delivery was rhythmic and deliberate, as with any folk tale learned by rote.

“The Lord was a man possessed of great beauty but small character. Seeing that his indiscretion was sand in an hourglass, and that his wife would soon come to understand the nature of his relation with their servant, he waited until a great storm came upon their vessel and then he threw Undine into the ocean. Undine sank, and began to drown, for her own human lungs were not equipped to breath water.”

John found himself hypnotized.

“Did she weep? No. Did she rail against the heavens? No. Did she bemoan her helplessness and wait for death’s embrace? No.”

Here Mycroft paused, and John leaned forward, willing to ask the expected question. “What did she do?”

“She cultivated within her an anger deeper than the blackest places of our own ocean. Inside her body the woman Undine drew forth a fury blacker than the void, blacker than the deep sea trench. It was an anger so complete that it manifested as power and Undine said to herself, _would that I was a fish._ And lo! She transformed.”

John raised an eyebrow, unwilling to break the spell of the tale but incredulous nevertheless. “She… willed herself to turn into a fish?”

Mycroft nodded, eyes crinkled with good humor to show that he acknowledged the far-fetched nature of the tale.

“Yes, for her anger was an engine that could not be contained. However, a woman may not simply become a fish; the transformation of Undine was incomplete.”

John saw where this was going. “She is the first mermaid.”

“Verily so.”

“What happened then?”

“She rose up from the waves, which knelt before her fury. The ocean was sympathetic to her. She called to the lord where he stood on the deck, and he could not resist her Song. She smote him and with new strength rent the bones from his puny human body, and then for her final act of defiance she surged onto the vessel and claimed his wife as her own.”

John laughed aloud in surprise. “Good for her!”

Mycroft’s nictitating membranes flicked over his slate-blue eyes.

“Undine and her new bride descended into the ocean, the first of our kind. Later she birthed the first clutch, which she banished into the ocean for she wished for no reminders of the lord who had betrayed her. But her children begged to know their mother’s name, and she said unto them, ‘I am Undine, and so are you. Now begone from my sight and live your lives as you will.’

And they did.”

John cleared his throat, processing this tale. “So... the undine are descended from humans.”

Mycroft shrugged, coasting his palms over the water’s surface. “That I doubt.”

“But you just said -!”

“It was a folk tale, John. Our origin myth is precisely that - a _myth._  No one knows if it is true or not. All that is known is that our young hatch speaking the languages of humankind, and that we are the undine.”

“Well. Serves the lord right if you ask me; who throws a woman overboard to hide their indiscretion? True or not, that was amazing.” John said honestly.

Mycroft bowed slightly, and John saw his gills fluttered with pleasure.

“It’s a shame that you don’t have a city, I should have liked to visit it,” John added.

“I agree,” murmured Mycroft. His expression was saturnine. “But these things take time, and mine own people are difficult to control.”

“Perhaps you shouldn’t try to control them.” John said carefully.

Mycroft snorted patronizingly. “We cannot continue to ignore each other, cannot continue to live and die largely alone. The waters are changing, and you humans grow bolder every decade. We must unify and pool our strengths -”

John raised both eyebrows mutely.

Mycroft scowled. “You’re human. I do not expect you to understand.”

John shrugged, and his apathy seemed to irritate Mycroft, who drew himself up taller in the water where he sat. Sensing a need to change the course of their dialogue, John asked again, “Why did you call Sherlock after… well, after Olizarat?”

Mycroft blinked in surprise, focusing rather on the wrong part of John’s inquiry. “He told you her name?”

“Yes?”

Mycroft’s eyes narrowed. “What else did he tell you?”

“That she was a Named One, and that Olizarat isn’t the only leviathan in the sea.”

Mycroft sighed and looked skyward as though hoping an angel would descend and relieve him of all responsibility to educate John. “She is not. There are eight - what did you call them?”

“Named Ones?” hazarded John. His brow pleated worriedly. _Eight? That is eight too many, if you ask me._

“It’s as good a translation as any, I suppose,” Mycroft conceded. “She was known as Olizarat the Destroyer.”

John was quite glad Mycroft had paid a visit this day after all. It seemed like the elder undine was willing to answer a plethora of questions that John hadn’t even known to articulate, and his mind was greedy to receive.

“Olizarat the Destroyer,” echoed John softly. The name seemed fitting in his experience. He felt distinctly the weight of the leviathan’s tooth between his pectoral muscles, and it took on a new meaning for him. “Who… who are the others?”

Mycroft spoke in a monotone recitation: “The Named Ones are described as the Destroyer, the Consumer, the Listener, the Peacekeeper, the Haunter, the Enslaved One, the Executioner, and the Mother. Olizarat is dead, and rumor has it that Shatulk the Haunter fell to a sorority pod of mine own sisters six moons ago.”

“The Peacekeeper sounds nice,” tried John, shifting his weight to his other leg and making sure that the bream didn’t slip off the point of his javelin.

Mycroft shook his head.

“An understandable but false conclusion. Not all of the Named Ones are malignant, but the Peacekeeper trumps Olizarat for malevolence any day. At any rate, John, I sense Sherlock has arrived. If I do not greet him immediately, he will assume I was seducing you.”

They both winced at that unwarranted mental image.

Mycroft turned to go, but then he hesitated and looked solemnly over his shoulder at John. The sun was blinding on his oxblood-and-eggshell striped scales where they bobbed just below the surface.

“Mine own offer still stands.”

“I said no,” growled John, agitated at being presented with temptation once more.

“Then I leave. Good-bye.”

“Mycroft, wait! I, ah. Thank you. For helping with, with this.” John grabbed the tooth around his neck and let it drop again by way of explanation.

Mycroft’s eyes narrowed. He nodded, slipped into the ocean, and was gone.

~  ~

Sherlock came later, when John was enjoying fire-baked crabs and flaky cooked fish. When the overtone hum rolled up the beach, John licked the juices from his fingers and stood, brushing sand off his thighs. It was twilight, the moon rising. The fire cast red and gold light across the sand.

John checked the fire and fed it another dry branch. He got a moment of inspiration, then, and took a slow-burning branch out of the fire. Then he made his way down to the shore.

Sherlock had hauled himself much farther onto land than usual, much of his ink-black tail visible out of the waterline. When he saw John coming, he rolled onto his back and stretched languorously like a cat that knew it was being observed. John laughed, crouching near him.

“Pretty thing.”

Sherlock thrust his narrow chest upward in blatant invitation. John soothed his callused palm obediently over the smooth white skin, down the groove of his breastbone and back up to skate across the places a human would have had nipples. The undine sighed happily.

“John.”

“I brought you something,” said John, struggling to speak over the lump in his throat. _God, he’s beautiful_. _It hurts._  He wasn’t the kind of man to get emotional over a beautiful sunrise or sunset, but apparently seeing a living merman provoked within him an artistic appreciation.

Sherlock sat up with ease, using a pelvic fin to balance himself when he leaned closer. John presented the burning branch to Sherlock with a smile, and Sherlock accepted it delicately - like a woman taking a red rose. The gold light flickered on the harsh angles of the merman’s face, making his colorless eyes light up like prismatic suns.

“I admit I have not seen fire under these conditions. It interests me,” murmured Sherlock, fascinated by the pattern of the flames. John, for his part, studied Sherlock’s face, which was so human and yet so alien.

They leaned into each other, faces dangerously close to the flame. Then a serendipitous burst of wind snuffed this final barrier, and they kissed. Sherlock’s lips were generous and soft. John sighed contentedly when they pulled apart, leaning his forehead against his lover’s and feeling cool breath tickle his beard, which he had managed to pare down a bit.

“Mycroft came,” John said at last.

“Mm,” agreed Sherlock. “Mine own busybody brother. Did he offer to take you away?”

John tensed up and said nothing. But he Sherlock’s mouth curve into a smile.

“He told me that you refused. Why?”

“I don’t trust him,” said John, and since he was uncomfortable now he pulled back. Sherlock whined so faintly that John might have mistaken it for a noise of the ambient ocean if he weren’t by now so familiar with his vocalizations.

“Do you trust me?” Sherlock wanted to know. He stared at John intensely, quivering with hope.

John felt strange. He did not want to answer that question, so he stared stubbornly back inland at the silhouettes of dark trees and brush on the island. Sherlock dropped his head to John’s neck, pushing gently with his nose to encourage John to make room for him. John tilted his head to the side. Sherlock kissed the side of his neck.

He cupped the opposite side of John’s jaw as he did this, thumbing his whiskers, and then began to lick John’s neck. It was a slow, obsessive motion that rather brought to mind a mother cat. It tickled and aroused in equal measure, and John squirmed. Sherlock chuckled. Then he opened his mouth and gently bit down.

John could feel the pointed tips of Sherlock’s teeth indenting his skin; he spread his legs in subconscious invitation. Sherlock rested his hand proprietarily on John’s groin.

“Nevermind,” purred Sherlock, baritone so deep that John felt it in his bollocks before he processed it in his ears. “Tomorrow I would like to show you something, mine own little one.”

“What is it?” growled John, trying his damndest not to push his cock into Sherlock’s hand, which was a pleasant weight.

“To tell you would spoil your reaction. And oh, you are so very _responsive._  I should like to see you pleasure yourself.”

John forgot how to breathe. Apparently this was a recurring theme in their acquaintanceship.

Sherlock’s voice dropped into a conspiratorial whisper. “Do you remember when I took you in hand, in the early days? You were so tense. I could feel your need, aching for release. You wouldn’t touch yourself… I had to take care of it for you.”

Sherlock’s hand lifted slowly away from the heat of his groin and John loosed a strangled grunt of protest. Sherlock chuckled. Long webbed fingers dipped beneath his kilt, drifting feather-light across the cinnamon hair below.

“Your own skin changes color when you are filled with desire. You’re so warm in this secret place… mine own small sun. Mmm, yes. Touch yourself now.”

John wet his lips. He made eye contact with Sherlock, heart thudding like a war drum, and very deliberately rucked up his kilt for better access. John licked a stripe up his own palm and curled his fist around the steel heat of his erection. Sherlock’s pupils dilated visibly and his breath hitched.

“Oh, _John_ …”

“Where are you taking me then?” huffed John. He stroked himself, pleasure tightening already behind his navel.

“Mmmm. The ocean is filled with many horrors, but it has beauty beyond your comprehension as well,” Sherlock murmured thickly; it was evident he was torn between watching John's face and observing the proceedings below.

The sound of Sherlock’s voice was cool water on a parched throat. John’s breathing raced and he did not reply. Looking at the sleek, wet curves of Sherlock’s astounding, incomprehensible body where he strove to curl in close, John thought, _Oh I comprehend it, my silly great fish._ He opened his mouth to say this, but his paroxysm came upon him unexpectedly and he instead emitted a deeply satisfied groan and painted his own belly with spunk.

He flung himself back onto the sand and gasped for air, a forearm dropped across his eyes. Sherlock crooned approvingly and moved so that he was holding his upper body above John’s, palms planted in the sand on either side of his ribs.

“Will you come?” asked Sherlock softly.

“I just did,” gasped John, chest still heaving.

Sherlock pinched his nipple and twisted it gently. John grunted. “ _Guh._ Yes, I will come.”

Sherlock smiled.

~  ~

It was still dark out when John woke.

Sherlock was capable of doing something with his voice that registered as a prickling sensation just underneath John’s skin, a full-body shiver not unlike being tapped with thousands of tiny fingers all at once. At first, this pseudo-Song had been frightening, but now John was acclimatized to it. He stumbled down the shore, nearly tripping on the clotted sand, and waded into the ocean and into the wet circle of his lover’s arms.

Sherlock drew him down and inhaled the sleep-warm scent of him.

“Mm, you’re so warm after you sleep,” the undine rumbled, shoving his nose into John’s oxter and inhaling deeply.

John lifted his arm tolerantly as Sherlock continued to invade his intimate spaces, smothering a yawn in his palm. There was no point in telling Sherlock to observe social boundaries, for that was a lesson that would never stick.

“Where are we going?”

“Below.” Sherlock spoke into the crease of John’s elbow, taking the thin skin there between his needle teeth carefully. He did not elaborate.

He took John out into the deep ocean. The journey out took long enough that the cool breeze on John’s face brought him to wakefulness. This far out, there were no visible landmarks despite the benefit of the now-risen sun. Just an endless expanse of steel-colored sea foam on cerulean waves. So when the undine slowed and eventually stopped, John released his grip and watched Sherlock swim in a wide circle around him. 

John squirted seawater out of his mouth at Sherlock. “Are we there? What do you want to show me?”

Sherlock’s face emerged. The water clumped his dark lashes together where they framed seaglass eyes. “How deeply can you dive, John?”

“Not sure,” John replied cautiously. “Are we testing that today?”

“It is necessary. I will breathe for you once we have gone deep enough.”

John studied him.

“Could be dangerous,” Sherlock added.

John felt a thrill surge through him, and his nipples tightened with a different kind of arousal. Judging by Sherlock’s smirk, John had not succeeded in keeping his expression unreadable.

John took a few minutes to slow his breathing. Then he emptied his lungs of most of their air and plunged below. He had discovered that he could dive more deeply if he exhaled first.

He’d gotten quite good at it.

He closed his eyes and focused on achieving the maximum depth he could himself, slicing down through the water like a jackknife. Of his own power, John achieved about thirty feet of depth and then Sherlock appeared, cupping his big hand around John’s chin and lifting his mouth to deliver air. Inhaling this far below felt peculiar. John was particularly conscientious of the fact that his lungs were opening outwards against some invisible pressure, like a nocturnal flower. He grinned at Sherlock, who was subtly peacocking for John by showing off his plumage to best advantage.

Wee plankton sparkled in the depths like tiny mobile constellations around them.

Sherlock presented his back, and John gripped his dorsal fin. John was happy to let Sherlock tow him. Down, down, down they spiraled into the deep.

John felt the temperature change as they descended, and observed as the microscopic sea creatures thinned until the water was as clear as a pane of glass. It was as though they were floating in the sky; only the occasional bubble ruined the illusion of suspension. A dog-sized cod jiggled past them in the water, the flat black-and-yellow discs of its eyes displaying John’s own reflection.

A school of fish exploded out of the deep and hurtled past, parting fluidly for the obstructions of man and merman, there and gone again as quick as a summer storm. John wondered what had startled them. The answer soon appeared, manifesting from deeper waters. It was Mycroft, and John stared. For although he _had_ seen the elder undine underwater before, there had been a leviathan involved and no time to appreciate him. Underwater, Mycroft was just as magnificent as Sherlock, if in a different way. Where Sherlock was beautiful and seductive, Mycroft was majestic.

He clicked to Sherlock. (John thought it sounded a bit pompous.) Sherlock arched his back haughtily and clicked twice in response.

Refusing to be left out, John clicked, too.

Both mermen whipped their heads around and stared at him, and John lost a bubble laughing at their stunned expressions. Sherlock frowned. He dipped in close, sealing his lips over John’s to replace the lost air. In his peripheral vision, John saw Mycroft stiffen. _What? It’s not like I can breathe water._

John ghosted his hand against the blade of Sherlock’s cheekbone, thumbing over the delicate skin beneath Sherlock’s eye and staring straight into that atavistic squiggle of a pupil. The undine’s face was impassive, but John knew him well enough by now to know that a blank expression did not necessarily mean a lack of opinion.

John leaned in and rubbed his cheek against Sherlock’s in gratitude, smirking at Mycroft’s affronted click. Mycroft could sod off. Sherlock went very still in surprise. For John, any extra motion underwater was costly. The deliberate cheek-bump was a transparent effort to communicate to Mycroft that he and Sherlock were intimate, and judging by the sour expression on the elder undine’s face, Mycroft understood.

After a beat of hesitation, Sherlock cupped the back of John’s head, skidding his cheek against his whiskers. Mycroft rolled his eyes at their unsubtle display. Then Sherlock took John’s hands and settled them very firmly upon his own dorsal fin. John had just enough time to secure a vice grip on his lover’s scaly derriere before Sherlock took them deeper.

After a pause, Mycroft followed.

It was in this way that they descended to an impressive depth. The water immediately surrounding the unlikely triad was lit by the distant sun, and the depths below seemed endless, a velvet-blue abyss. John’s ears popped. The air Sherlock could breathe for him was salty and wet. It was hard to get a deeply satisfying breath, and it was colder this deep. _It’s not unbearable,_ thought John. _I do believe I can go deeper._

Had any other living human ever gone this far before? Was he the first person to ever achieve this kind of depth? John watched the bunch and flex of lean muscles in Sherlock’s porcelain-pale back. He found himself hypnotized by the subtle glitter of black scales on Sherlock’s lumbar area. To their left, Mycroft swam like a one-merman parade; a rattle of fingerlike striped fins fanning open and closed with his locomotion.

 _What incredible beings,_ John thought. Had he been on land, he might have let out an exhilarated whoop. _Oh, but my life has taken a turn for the peculiar._

Apparently this was their destination, for Mycroft and Sherlock drifted to a halt. John tapped Sherlock’s shoulder. Sherlock turned indulgently and their lips met for a life-sustaining kiss. This exchange was so well-practiced that there was no awkward nose-knocking or teeth clunking; Sherlock leaned to the left, and John leaned to the left, and their mouths touched gently and opened in perfect synchronicity. Black curls as soft as pondweed tickled John’s cheeks.

John could practically _feel_ Mycroft staring. He drew back quickly and glanced at the other undine. John caught a glimpse of a nostalgic expression on Mycroft’s face just before it was replaced by a mask of regal impassivity. John wished he could speak.

Both brothers had unfurled their fin plumage. John got the feeling that they were using these fins as a cat uses its whiskers. Sherlock’s aural fins were perked, eyes squinted with concentration as he listened, or felt for some vibration in the water that John was not privy to. So John waited, periodically taking his air from Sherlock. After a short spell in which John entertained himself by doing slow flips (both undine watched him with amusement), the brothers’ body language changed quickly.

A giant head appeared from below, twisting like a periscope on an unfathomably long neck. It seemed to be some kind of marine lizard, although John had never in his life seen a reptile like this. Its neck was so unfathomably lengthy that John could not actually see _where_ it attached to a body, for the murk of the deep ocean obscured its termination. It had opalescent white scales.

 _Another leviathan! A Named One?_ John whipped around to see what Sherlock thought of this.

The undine was watching John’s reaction carefully with his sloe-eyes.

Mycroft left them and approached the leviathan. It turned its huge head to focus on him. John might have gasped in water if Sherlock hadn’t forced their mouths together for air. For now that Mycroft was next to the leviathan, John got a sense of its size. Olizarat had been huge, but this thing was _colossal._ Its head alone was nearly twice the size Olizarat’s entire body had been.

It had two pairs of eyes on either side of its head. As John looked on in astonishment, these four eyes blinked their nictitating membranes asynchronously. The leviathan’s head was richly ornamented in short tentacles, like the whiskers of a catfish. A particularly thick frill of these whiskers hung down from the Named One’s chin. A generous mane erupted like a sunburst behind its head, a gently waving forest of ropey white strands. John thought he could probably swim into that forest of whiskers and never be seen again.

Initially, John had taken this Named One for a lizard, but upon more measured inspection the bone structure called to mind something more equine.

Mycroft floated in front of the Named One’s face, palms outstretched. The leviathan reached out with a whiskery appendage. Mycroft caught the tentacle as it drifted close, and the moment they touched - _like a handshake_ , John thought to himself - the Named One’s appendage began, well, it began to _glow_.

_Oh my god. Are they really communicating? This is incredible, I never - !_

Mycroft touched the leviathan’s snout, right next to where a slitted nostril was cinched tightly closed. They leaned in close in silent conference. Then Mycroft looked over his shoulder at them with a nod. John grabbed Sherlock’s hand and squeezed. Sherlock blinked and looked at the place they touched. After a moment, Sherlock’s big hand slowly tightened in his.

He jerked his chin in the direction of the leviathan as if to say, _go say hello then_ , _we haven’t all day._ John’s skin felt strange. Itchy, almost. He shook off the queer feeling and used his feet to push off of Sherlock’s tail and glide in close to the magnificent animal with whom he was to be acquainted.

Mycroft looped around the leviathan’s huge snout. He perched on the flat plane of its forehead. The leviathan tolerated this with no more reaction than a horse would give a fly, although the top pair of eyes attempted to track his movement. This Named One seemed to be a gentle giant, the polar opposite of Olizarat’s ferocity. Armed with curiosity and a fresh lungful of air, John reached out. The leviathan’s hide was rubbery and smooth. He felt a tickle around his ankle where a tentacle lightly looped, a polite tug of greeting. He stared curiously into the glassy pane of an eyeball.

 _Hello_ , thought John with a slow and spreading smile.

To his shock, the creature responded with a loud, bovine low.

 _Oh! Can you understand me?_ he thought intently, filled with an absurd and boyish hope. Could this creature read minds? John wouldn’t be surprised. He had experienced so many fantastic things since the night he fell overboard. _Cor! You must be huge, with that great long neck I can’t even see your body at all from here._

The creature tightened its tentacle around his ankle; John glanced down and did a double-take. The tentacle was glowing. Struck with an inspiration, John sunk his forearms up to the elbow in the catfish-like beard of whiskers. They began to glow faintly as well. It brought to mind the secret light-up lake that John had discovered in Sherlock’s grotto.

_Can you hear me?_

All four of the leviathan’s eyes focused on him.

John grinned like a madman. _You can! Amazing! Fantastic!_ _Oh, I need air._ Sherlock nudged into John’s space long enough to deliver breath and withdrew. Anxiety tightened the corners of his generous mouth, and he glanced over at Mycroft. The lionfish undine shook his head gravely, jabbing a clawed finger skyward. The message was clear.

Sherlock hesitated, then reached for John.

 _No!_ thought John, _We have only just arrived. I’m not going back up yet, it’s too soon._

John shrunk away from Sherlock’s half-hearted reach. He grabbed the nearest tentacles and began to pull himself briskly along the leviathan’s long face. It probably looked ludicrous, but he did not care. No merman was going to make him surface a second sooner than he intended to. In this way, John crawled like a crab until he was floating right in front of the Named One’s dual pair of eyes.

Sherlock followed him anxiously, brushing his gossamer fins beseechingly against John’s legs. John ignored him, and ignored the fizziness in his joints. He chalked the slowly intensifying itchiness up to excitement.

The leviathan’s vertically-stacked pair of eyes were liquid black. The lacrimal duct, the pink fleshy bud on in the inner corner of the eyes, was the size of an apple. It looked soft, and John reached out and touched it on a whim. It was moist and squishy, and the irritant made the Named One blink rapidly.

 _Beg your pardon_ , John thought.

The Named One tolerated having its eyeball touched with remarkable calm. In fact, this creature was possibly the most welcoming thing John had ever encountered in the ocean.

Sherlock clicked agitatedly, stroking John’s arm to get his attention. John jerked his arm away. He was not ready to go up yet. How could he be expected to return to the surface so soon? No, the undine would just have to wait.

John swam over to the nearest tentacle he could reach. This he gripped and he projected a message again, wondering if he would be understood. _Do you have sharp teeth? Do you live all alone down here? My name is John! John Watson._

Much to his delight, the Named One began to sing: long bugling notes were flavored with brief squeaks at a high frequency. It opened its mouth obligingly and John pulled himself along its jaw and looked inside the cavernous white maw. It had a flat tongue and tiny little teeth lining its mouth, barely the length of John’s finger and numerous. Many of them were missing.

 _I bet you’re as ancient as the ocean,_ John thought.

His lungs were beginning to burn; he had waited too long between breaths. He turned to look for Sherlock. He almost collided into him, for the undine was towering ominously over John in the water, fins flared out. John climbed up Sherlock’s body, gripping with nimble fingers and toes, and leaned in to take his air.

Sherlock refused to open for him.

Betrayed, John drew back in astonishment. His lungs screamed in protest. _What the hell are you playing at, Sherlock? This is not amusing. I need air._ But the undine’s face had gone frosty, pupils transformed to the W-shaped feral squiggle. _Oh god, not now. Please not now. This is dreadfully poor timing for this nonsense!_

A cramp stabbed in his leg. John coughed out a bubble, folding in over himself where his abdominal muscles seized. He didn’t have much time left. One of the Named One’s whiskers curled around John’s wrist - and flinched away as though John’s skin were magma. The leviathan moaned sorrowfully. This seemed to bring Sherlock back to himself. His eyes refocused and he snatched at John in alarm.

He dispensed air with a panicked flare of gills.

John sucked in the air greedily.

The cramp in his leg subsided somewhat, but the strange sensation of fizziness in his blood did not dissipate. He needed clean, dry air. John realized that he needed to return to the surface, and _soon._

Desperation truncated a lengthy farewell, but John squeezed one of the Named One’s multiple whiskers, which politely squeezed back and released. He made to grip Sherlock’s dorsal fin, but to John’s horror his fingers would not tighten. Mycroft appeared, fluttering nervously. He and Sherlock exchanged a grim look.

This was not reassuring.

In an instant, John found himself wishing nothing more than to rise to the surface. Sherlock looped his arms beneath John’s and began a controlled ascent. The undine swam in slow ellipses toward the sun. But this route seemed unnecessarily circuitous to John.

_My feet feel numb. This is no time for dawdling, Sherlock! I know you can get me there faster._

Never a man of idleness, John pulled free, intending to swim of his own power to the surface. But Sherlock caught him before he had ascended more than a foot or two. John growled and tightened his grip warningly on Sherlock’s arm. Unfortunately, John needed a fresh lungful of air and the fact he had to suddenly crash his mouth against Sherlock’s - _not a kiss_ \- undermined the effect of his furious scowl. The briny breath was unsatisfying and his lungs stuttered with need.

Why was Sherlock preventing him from shooting to the surface? Even Mycroft condoned this cruelty, floating between them and the seductive brightness of the distant surface.

 _Oh you cruel, cruel bastards!_ thought John furiously, a white-hot fury coming over him. _Am I to die here, tormented by fickle merfolk? To think I ever trusted you._

Had he the energy, John might have railed against Sherlock during these dizzying intervals of breath and ascent.

At one point he suspected he had drifted upside-down entirely, and from this angle the Named One was visible below: hundreds and hundreds of meters warped by perspective so as to seem within grasping distance. With a detached sort of interest, John noticed that this leviathan had a humped back. The bony lumps of its vertebrae protruded like clenched fists trying to punch free of the rubbery skin. These vertebrae surged up and down as it swam, flexing its four long, paddle-shaped flippers. Their motion brought to mind giant oars sweeping through the deep. Its tail was stubby and short in comparison to the neck, which was extended as it swam - twice again the length of its gargantuan body.

 _Am I dying again?_ John thought deliriously, barely registering when Sherlock provided him another breath. It was on the heels of this thought that whiteness encroached in John’s vision. He did not feel well.

Not one bit.

His body was not listening to his command to swim. His joints ached. Sherlock’s beautiful face came into focus inches away, brow furrowed and eyes huge with concern. Cool hands cupped his cheek, and John’s head lolled into the touch.

At last they broke surface and John breathed. It was enormously satisfying, a cold gulp of crisp _dry_ air and he was grateful for it. Unfortunately, with the dry air came a sudden and merciless bout of nausea. He thought he would vomit. Sherlock and Mycroft both watched anxiously, webbed hands supporting him in the choppy waves. Sherlock was speaking, but John’s ears rung with a tinny shriek and he could not understand him.

“I’m fine,” John told them.

Except it must have come out wrong, because both Mycroft and Sherlock stiffened in abject alarm. Mycroft’s mouth moved and he said something to Sherlock. Sherlock refused to look away from John, though, and the last thing John experienced before consciousness fled was the bright glint of sunlight on black scales and the bite of cool wind on his face.

~  ~

  
The first thing John did upon awakening was vomit.

And vomit.

And _vomit._

He had never felt quite so nauseous in his life, and when he was done he gasped in breath and shoved his face into clean sand with a miserable moan. His muscles ached. He was parched. John felt like hell, and if his joints weren’t screaming in pain he might have described his own condition as ‘like a living corpse’.

“John!” a deep baritone rumbled in his ear.

John turned his head, spitting the sand that clung to his lips, and was surprised to see that Sherlock was on land too. It was not difficult to deduce how he had gotten there. John had obviously fallen unconscious, and judging by the deep grooves in the sand cutting a path to where he lay in the shade of a rickety palm, Sherlock had dragged him up onto dry land.

“Sherlock? What the hell are you doing up here?” he croaked. (At least, he tried to. What came out was probably closer to, “ _Sh’lock? Wharra hall’re you do hurr.”)_

“Don’t talk. You have the water-sickness.”

John sat up slowly. Sherlock tracked the motion. Ever the Englishman, the first thing John did with his newfound autonomy was to politely scuff sand over the damp mess he had made upon awakening. His nausea receded to a minimally threatening level and John took a moment to reacquaint himself with his body. He started by wiggling his toes. Those seemed to be in working order. He twitched the muscles of his calves. Fine. He flexed his knee - _ah, cor damnit that stings._

“My knees hurt and my head aches,” John told Sherlock. “What are you doing up here?”

Sherlock ignored the pertinent question. “You must focus on breathing this dry air now, John. Do not waste words.”

John agreed and fell silent. They had to be about sixty or seventy feet inland. For a merman with a tail that weighed god knew how much, that was no insignificant feat of athleticism, and once again John found himself in awe of Sherlock’s supernatural strength. 

Sherlock must have been out of the water for a while. His hair had dried to soft black ringlets. His neck and rib gills were dry, and curling up slightly at the edges. He had coiled his enormous black tail to the best of his ability. His fins were strewn haphazardly across the shady sand around his tail, like someone had dumped out an armful of clean white sheets.

John looked out across the beach. Down by the ocean, Mycroft had actually deigned to pull partially onto shore and was watching hawkishly. John raised an arm in acknowledgment and Mycroft visibly relaxed. _Probably glad I finally woke up, and that Sherlock can go back to the ocean where he belongs_. 

"What are you thinking coming out so far onto land?" reprimanded John. His voice came out like mummy dust.

“Don't speak. I will answer the questions you have now,” Sherlock told him. Apparently, John wasn’t expected to articulate these, for the undine gave no pause. “You have the water-sickness. I have seen it before, and deduced its cause: it is something about coming to the surface too quickly. At first, I thought it had to do with the depth of the water, John, but evidence suggests that is a false conclusion. Human bodies are inefficient -”

Sherlock’s pointed teeth clicked shut. He glanced at John’s face before inhaling to plow ahead - but John wasn’t going to let the undine get away with it.

“Sherlock? How do you know about the water-sickness?” John whispered gravely.

Sherlock went very, very quiet.

“Did… did you experiment on humans you found?”

Sherlock’s dorsal spines flexed anxiously. He said nothing.

“Oh my god.” John whispered, falling back onto the sand and staring at the flawless blue sky through a lace of green palm fronds. Sorrow for the lives lost to Sherlock’s cruel whimsy filled John.

Heat stung the corners of his eyes.

“You don’t understand, John,” Sherlock said stiffly. “I just wanted - I had to see. I had to know. Aren’t you in the least bit _curious_ as to the limitations of your own body? Humans are fascinating! How can they hold their breath so long, how can they swim and also walk on only two legs?”

John focused on keeping his breathing even.

Just breathing seemed to be making the pain in his joints less. Thank god.

Sherlock continued.

“I don’t regret it,” he told John. He sat up and stared down imperiously. “If I hadn’t done it, I wouldn’t have known how to keep you safe at that depth. It was a calculated risk.”

John did not want to be having this conversation. Clearing his parched throat, he offered an olive branch. “That was a Named One, wasn’t it.”

Desperate for a connection, Sherlock latched onto this opportunity with poorly-disguised relief. “Yes. He is known.”

“What’s his name?” John whispered, letting his eyes fall closed. He ran a sandpaper tongue over his chapped lips.

“He is the Listener. Lahosiel is his name.”

_Sherlock. Mycroft. Olizarat. Lahosiel. The undine, the Riptide. It’s all just so fantastical, like - like a storybook. I feel like the character in a storybook. A frightful one. John Watson, the only human amongst a stable of mythological monsters. Where is the life I once knew? It seems but a shadow of a dream._

“Sherlock?”

The undine shifted on the sand, leaning over John. John opened his eyes to check his companion’s position, and wished he hadn’t for Sherlock looked angelic. Sunlight fell behind his head, illuminating dark curls at the edges like a golden halo. He laid his hand on John’s chest, smoothing his webbed fingers over the crisp gold hair.

“Yes, John? There is water here when you’re ready, in this shell. It is the kind you drink.”

“That was not what I was going to ask. I should like for you to promise me something.”

Sherlock’s hand started to slide away, so John caught it. Sherlock had enormous hands, possessed of a fine-boned delicacy that beget worship. John lifted the undine’s hand to his mouth. He breathed warmly upon those knobby knuckles, and spoke into the fine webbing.

“Promise me that you will never kill another human being again.”

John saw the distant figure of Mycroft sit up in alarm. Sherlock eyed John frostily, but did not take his hand away.

“I make no promise thus.”

John stared up at Sherlock through the gold lace of his own lashes. He took the undine’s fingertip between his lips and sucked very lightly.

“ _No_ , John. I must have the freedom to kill.”

John touched his tongue to the tip of Sherlock’s finger, swirling it gently around the pad and ever cautious of the hooked claw. Sherlock made a strangled sound. He let his eyelids drop to half mast and then let fall his most devastating weapon. 

“Please,” he growled. John wasn’t entirely clear himself what he was asking for, anymore.

Sherlock actually _keened_ under his breath, his entire great body trembling with the arousal John had awoken in him. He mounted John carefully, planting his palms on the sands on either side of him. He dropped his head down to rub his lips along his clavicle. He opened his mouth and took John’s exposed throat in his teeth, mouthing it in tender facsimile of some rending beast.

“Oh, cruel, cruel, unfair,” Sherlock accused in a syrup-thick baritone.

John felt his vulnerable throat bob against the threatening pressure of the undine’s teeth. “I just want you to promise me, Sherlock. Don’t kill any more _humans_. That’s all I want.”

Sherlock’s mouth went soft on his Adam’s apple, needle pressure replaced by gentle suckling. John groaned. His head ached too much to achieve an enthusiastic erection at the moment, the fizzling of his joints an unpleasant distraction, but he delighted in the effect he had on his lover nevertheless.

“Am I to render myself defenseless? Humans are dangerous, John. _You’re_ dangerous,” purred Sherlock, snuffling down John’s chest to nuzzle at the flat disc of a nipple. “I promise not to kill _you_.”

“Mm. Not good enough,” said John. He threaded his fingers into soft black curls.

He steered Sherlock’s face down, pressing his head into the muscle of his pectoral until the undine sucked his nipple. The long, thick weight of Sherlock’s cock made itself known against John’s hip, hot and slick. John hoped Mycroft wasn’t watching, but a wild part of him couldn’t care less what the elder undine thought.

“Sherlock.”

Sherlock released John’s tormented nipple, which he had been biting at until it blushed red. “Will that please you so much?”

“It would,” John said.

Sherlock propped himself on his elbows over John’s torso, gazing into his eyes. His breath was cool and smelled like distant rain.

“Very well. I…” the undine paused, looking distinctly uncomfortable. But John smiled encouragingly, and Sherlock finally said, “I... promise not to intentionally kill any more humans.”

The wind stopped blowing. The noises of the ocean ceased with supernatural poignancy. The only sound was a faint gasp from the shoreline - and nobody cared what Mycroft thought. John cradled Sherlock’s cheek, wishing he didn’t feel so ill that he might kiss his companion. “You brave beauty. Thank you.”

And gradually, the noises of the sea resumed.

~  ~

 _* Lahosiel the Listener’s body type is loosely inspired by an_ [ _ elasmosaurus  _ ](http://4.bp.blogspot.com/-7n8jS1twg2c/UeD1IwqI8mI/AAAAAAAAqHA/C38LJr75v5A/s1600/large_nicholson_plesiosaur.jpg) _, a plesiosaur from the Late Cretaceous period._

 

**Notes for the Chapter:**

> As always, you can look for update information on [my blog](http://jinglebellfic.tumblr.com/tagged/riptide-lover), since I'm no longer able to answer questions of that nature in the comments. There's also a [a playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I listen to while I write and I'm always looking for song recs.
> 
> Anyways, the pieces are at last falling into place for a big plot arc and I am feeling excited! I am going to feel so satisfied when I finally get to whip the curtain off this thing, I swear to god. Happy Christmas, my friends, please share your thoughts and talk amongst yourselves in the comments freely!


	13. Riptide Lover [Part I]

**Notes for the Chapter:**

> This segment was so long I had to break it into two chapters. I was originally intending to make everyone wait to read both parts at once (Chapter 14 is still a work-in-progress) but then I realized TODAY IS INTERNATIONAL FANWORKS DAY. To celebrate, please have an early update. Enjoy!

Sherlock returned to the water and left John to recuperate in solitude.

The water-sickness abated after a good night’s sleep, although John couldn’t keep his usual raw fish down. He lay quietly in the sand, observed rain-pregnant clouds, and felt sorry for himself. Eventually, the clouds broke and produced a gentle drizzle that reflected the sun like the Crown Jewels.

John stood and stripped off his kilt. He left it puddled in the sand. He stretched, reaching heavenward as though he could pull the clouds down. The rain trickled down his nude body, following the hills and valleys of his musculature and clinging in glassy beads to his beard and eyelashes. John stretched so deeply that he became reacquainted with muscles he had forgotten, until the strain made him tremble, and until whiteness encroached on his vision.

Then he slumped to his knees with a bone-deep sigh.

John tipped his head back and closed his eyes. Sherlock had promised not to kill another human being. According to the arcane conditions of existence for his people, he had to keep his word - or risk losing his supernatural gifts. Had the undine truly made this promise? For that matter, was John really on this island at all, or was it just a figment of his lonely imagination? If he opened his eyes, right now, and stared up into the rain - would he see the smog-wrapped buildings of London, or the Mediterranean sky?

He did not open his eyes.

He did not want to see the answer.

John wondered if he would ever see London again, his birthplace and home. How was his sister? What had become of the crew on the _HMS Endymion_ ? Were the experiences of the past couple months genuine, or were merfolk and leviathans just the desperate conjurations of a cracked mind? The weight of Olizarat’s fang on John’s breastbone said no, but the fog in his brain said _you are going mad_.

Who _was_ John Watson?

The man on the island couldn’t be sure.

The rain continued. John ate coconuts and wandered at a leisurely pace, clad once more in his kilt with the ivory knife at his hip. He thought about Sherlock as he investigated the interior of the island. He counted his lucky stars that he had not met the same fate as Sherlock’s other experiments. He reflected in particular upon the night they met. Had Sherlock not given him breath, John would be dead. But when had he become so complacent in his own captivity?

And here, with no one to judge him or hear his deepest thoughts, John reflected on how his life had truly been. Before becoming swept off the ship, his life _hadn’t_ been particularly noteworthy. John’s penchant for pugilism aside, he had been a dependable sailor - rated Boy 1st Class, and marked “very good” as to his personal character and skills as a seaman. He had thrown himself into his career with the fervor of a man who was attempting to outrun his own mind.

He found himself making his way unconsciously toward the northwest part of the island - toward Sherlock’s grotto, which to the best of John’s knowledge, was inaccessible by land. There was thick brush here. The rain was so pleasantly light that the sea birds did not bother to seek shelter. The presence of the birds reminded John of his sister, who kept one as a pet.

He had spent the majority of his shore leaves with Harriet, who it seemed lived in a perpetual state of emergency. His sister was a thespian without a cause. John liked to think that his visits contributed to Harriet’s wellness of mind. When the time came to go back out to sea, though, it was John who was left emotionally bereft.

It dawned on him now that his indulgence of Harry’s theatrics perpetuated the cycle. There was no necessity for maturation on the part of his sister.But truth be told, John preferred focusing on his sister’s problems.

That meant he didn’t have to ruminate on his own discontent.

When he wasn’t throwing himself into his duties on board the frigate, John was subject to deep melancholy. He could see no future for himself beyond the path of the working class sailor, and yet he wished for more. How could a man break himself out of the lifestyle that had been thrust upon him since he was a stripling?

He ducked beneath a heavy green branch in order to progress. The foliage this far inland was significant enough to remind him of a jungle, the sort of place John had imagined exploring as a lad. Dappled sunlight speared through the sparse canopy of green, casting freckled shadows on the turf. The rain let up, the pattering sound of droplets striking leaves ending as abruptly as a fit of sneezing.

The scent, the colors, and the temperature of the air only served to emphasize in John’s mind just how far from England he was, and this led to contemplation of his present geographical location.

The _HMS Endymion_ had been on its way back to London from the Maltese port when the storm struck. Captain had chosen to set sail despite the ominous portents, for they were all eager for the familiar comforts of Deptford. They had been only a few hours out from port when the storm struck. John was swept overboard and encountered Sherlock, who had then taken him on a half-hour’s journey in an indeterminable direction.

From this, and the landscape of Sherlock’s island, John deduced that he was still somewhere off the Sicilian coast. Although he was familiar with these waters, John couldn’t postulate with as much precision as he would like. He had been on the sea for nineteen years. John had a sense for these things - a knack, if you will. He had learned to go with his gut instinct when it came to nautical matters. He wondered if the frigate had made it back home safely. Had any of his crewmates been claimed by the sea?

John prayed that no one else had been sucked overboard.

In addition to drowning, a man risked encountering mythological man-eaters in these waters. God willing, his peers had made it back to London safely. But did John really want to return to London? It seemed that home was a memory painted excellent only in hindsight. And if he did return, would John have the courage to live his life on his own terms?

Perhaps John was no longer to be a cork in the stream, hapless in the course of his own destiny. Should he get the opportunity to return to fog-wrapped Londontown, John would _make_ those bold decisions he never had before. He would _take_ those risks, the risks that he would not have before meeting Sherlock.

The problem lay with the merman. Of course.

This was Sherlock’s territory. He was king of his domain. It was impossible to escape the island, for the undine was too fast, too atuned to minute changes in his environment. John’s only hope would be to somehow acquire Sherlock’s consent to leave. But Sherlock had made no secret of his covetousness. To him, John was a pet. John was a novelty to be kept and contained.

Was there some way that he could… could _outsmart_ the undine? Trick him into a promise of some sort? Or perhaps Sherlock could be distracted, somehow - just long enough for John to endeavor the swim to the islet of bone.

To the dinghy berthed there.

To freedom.

John sighed and scrubbed his hand across his face, wincing at the scratch of his whiskers on the tender skin of the new scar there. If only these machinations weren’t _necessary_. If only Sherlock cared about anyone’s needs but his own!

Well.

That wasn’t true.

John couldn’t deny that Sherlock made an exception where he was concerned. By undine standards, Sherlock positively cosseted John. Sherlock breathed for him, fed him, risked his life for him, and - best of all - had ceased trying to murder him on a daily basis.

John rather thought this was a good start.

He reflected on his relationship with Sherlock. Sherlock, who sought John’s attention like a flower seeks sunlight. Sherlock, who thought nothing of bringing John to shuddering climax with the same hands that had torn a leviathan asunder.

John’s rational mind had denied his desire at first. But there had been desire from the moment he saw Sherlock, when all hope was lost and John’s dying thoughts were not _please let me live_ but instead _shame, what a pretty creature._ That taboo ember had been stoked to flame - and now?

Now, John was worried.

He knew himself well enough at thirty-two years to recognize when he was well and thoroughly infatuated.

John had come to terms with his own inversion, but now he was erotically enthralled by a merman, of all things, and that warranted some self-reflection. John desired Sherlock, carnally and - and there was a shadow of something else there, something beyond the erotic.

It was this unfamiliar shadow of a feeling that bothered John. He did not wish to drag it out into the light and examine it, for he was afraid of what he might learn.

It was one thing to fuck Sherlock, and another entirely to love him.

~  ~

Filled with more questions than answers, John Watson found himself wandering down the beach on an island somewhere in the Mediterranean sea, and it was then that he came upon a merman - _his_ merman, of course, not another heretofore unintroduced fellow. Sometimes seeing Sherlock still caught John by surprise, triggered some hindbrain terror.

John tried to mask the hitch in his step by hopping over a piece of driftwood.

Sherlock rolled in the crystal shallows, miles and miles of inky black tail twisting around itself and tangling in his billowing, veil-like fins, stirring up clouds of sand. Sherlock stretched his arms out toward John like a vain housecat.

He wriggled his fingers come-hither.

John couldn’t help but grin. “Seriously?”

“What?” Sherlock frowned.

John picked his way through the beach detritus and stopped at the edge of the water. He admired this display.

“Did you just _happen_ to be here, on this beach today, or were you looking for me?” John asked, planting his hands on his hips and raising his eyebrows. He was trying to sound perturbed, but even to his own ear his voice sounded equable.

Sherlock detected the pleased note in John’s tone and smiled back, throwing the wet curtain of his fluke over with a smack.

“I listened for you,” Sherlock confessed. “Your own footsteps are audible even from the sea.”

“They are not,” John disagreed. “I’m quiet as a mouse!”

Sherlock paused.

A furrow appeared in his brow.

“A mouse is a small animal, a small furry animal. Mice are very quiet.” John clarified.

Sherlock made an interested noise. It was the noise John had come to understand meant that the undine was committing a new human fact to memory.

“In truth, I seek you. Follow me along this beach, I have brought something for us.”

John’s heart leapt. Sherlock rolled suddenly and speared off into deeper water like a black-and-white arrow. John broke into a dead sprint along the shoreline to keep up. He skirted the island hem, delighting in the sudden explosion of activity, and did not find himself breathless when he caught up with the merman.

Sherlock had flung himself partially atop a large wooden crate that had been shunted just out of the water. It was draped in fresh black seaweed. John went to him, laughing and slapping his palms down atop the crate. Sherlock’s hands rested there, too. John noticed the merman’s gaze lingering overlong on the juxtaposition of his own long webbed fingers near John’s short human ones.

John cleared his throat and asked, “What’s inside, then?”

“I do not know,” replied Sherlock.

John’s heart thumped unexpectedly.

_He could have opened this when he found it, but he chooses instead to bring it to me in order that we might discover the answer together._

John chucked Sherlock’s cheek with his knuckles. The skin was cool to the touch and John lost himself for a moment in the texture of the scales on Sherlock’s zygomatic arch. His gaze followed the dash of fine scales back where they vanished behind dripping curls.

That was when he noticed it.

Sherlock’s aural fins had changed color.

Oh, it wasn’t much. Just a hint of seafoam green glimmering in the semi-transparent webbing between onyx spines, but John knew Sherlock’s body. He _noticed_. Curious, John tried to push aside the obfuscating black curls.

Sherlock jerked away with a hiss.

“Easy!” cried John, showing his palms.

Sherlock withdrew, slithering off the crate and into the shallows, where he coiled his great tail around himself in a roiling mass of night-sky scales. John climbed onto the crate and looked down at the undine in alarm.

Sherlock bared his teeth.

“Whoa there, whoa there,” murmured John, placating. “I don’t know what I’ve done this time, sir, but I promise you my intent was not to offend!”

The undine sneered.

“ _Sherlock_ ,” breathed John. He ignored the discomfort in his knees where the crate’s wooden slats dug in.

Suddenly John felt a bit lightheaded; he had to sit back and press his temples. He scrunched his eyes closed.

 _Oh, this is poor timing. I might be dehydrated_.

A moment passed, then wood groaned with the addition of weight. There was cool breath at his neck. John opened his eyes. Sherlock held himself up over John’s lap, looming. His tail trailed out to sea. His expression was difficult to read, and he was staring somewhere behind John, but his proximity could not be mistaken for anything other than concern. Prickly concern.

“M’fine,” John grunted. “Are you going to tell me what I did, that I might know to avoid committing such offense in the future?”

Sherlock lipped at the scar tissue on John’s shoulder. In true undine fashion, he did not properly apologize, but his tone hinted at contrition. “I… John, it is the onset of the lek.”

“The what?”

“The Riptide. I cannot escape mine own body’s whim. I feel it in the water, in the dry air, in mine own bones it encroaches.”

John’s breath caught. _The Riptide. The time when the nomadic mermaids venture into shallower seas to seek the company of mermen, as I recall._

“It’s already here?” John whispered.

“Yes. By tomorrow I imagine I shall be in the thick of it, and shan’t know relief for days,” groused Sherlock.

His voice sounded a little different to John, now that he was listening for it - a new layer of gravelly thickness to an already chocolatey baritone. John imagined the sound of this changed voice broken by gasps, punctuated by the wet slap of skin on skin. With whom would Sherlock take his pleasure? How would his mermaid lover - _lovers!_ \- take to John’s presence on the island? Would John have to go into hiding for the duration of the Riptide?

And why on earth did the thought of Sherlock slaking his lust with another undine cause John’s heart to pound with excitement?

He cleared his throat and said diplomatically: “Beg pardon, but what if your lover sees me?”

Sherlock watched him carefully.

“At this time of year, she would be liable to tear you asunder. But you are mine own little one, and it does not please me to see you harmed. I... will not be entertaining visitors this Riptide.”

John flushed. He searched Sherlock’s face and found nothing but sincerity, and a touch of resignation. He was not going to apologize for his presence on the island, he was not. Sherlock was the one who had caged him. It was _Sherlock’s_ fault that John was there at all, and by extension Sherlock was the one responsible for his own celibate Riptide.

_But… does it have to be celibate?_

Sherlock’s sleek, strong torso glistened with water droplets, black mop of hair curling fetchingly against the spray of scales cresting his sharp cheekbones. His plush lips were parted slightly and his eyes seemed greener than usual, pupils squat and on the cusp of transformation.

John opened his mouth to express an idea which was not yet fully-formed - and was interrupted.

“John! Let us look inside,” barked Sherlock. He slid off of the crate in order to hook his claws beneath the wooden slats.

John laughed aloud in surprise, clinging like a limpet as Sherlock groaned with the effort of prying open the lid with a grown man’s weight upon it. This proved to be no obstacle for the undine’s supernatural strength, and Sherlock soon tipped John over and onto the soft sand. John bounded up and pushed Sherlock out of the way that he might look inside first.

Sherlock surged up behind him and supported his weight on the edge of the crate, arms bracketing John’s body and torso pressing up against John’s naked back. He peered over John’s shoulder to see.

The crate was unexpectedly dry. Musty. It had been lined with tar. Inside was a large burlap sack filled to the brim with onions.

“Onions!” cried John, with far more delight than that word had ever warranted in his life before. “Look! And they’re hardly even wet.”

Sherlock snorted with amusement, turning his head in order to lick a hot stripe up the side of John’s neck. But John wasn’t interested in accepting that invitation, presently. No. John was interested in _onions_.

He dragged the burlap sack out of the crate, shoving with his back until Sherlock dropped away, and shuffled manically up the beach. He dumped out the contents of the sack.

Out onto the sand poured onion after onion, followed by Jerusalem artichokes, dried chestnuts, and a single mummified apple that by some miracle of preservation had not turned to jelly as the cabbages at the bottom had. This did not dampen John’s enthusiasm in the slightest. It was _food._ And it wasn’t raw fish or bloody coconuts! John ate the apple like a delicacy, chewing slowly in order to savor the dull, mushy sweet flavor.

He nearly wept when it was finished.

He was picking up an onion and peeling it quickly, fully intending to eat the damn thing raw, when a prickling sensation on the back of his neck alerted John to the fact that he was being observed.

“Yes?” John grunted, flicking papery onion skin off of his fingertips impatiently.

“There’s more in here,” Sherlock informed him with barely-restrained amusement.

John gave up trying to peel the onion and shoved it right into his mouth, biting deeply into the crisp flesh. He trotted back down to the waterline in order to see what else was inside the crate.

There was nothing. John looked up in confusion.

“There isn’t anything in here,” he started to say, but Sherlock kissed him and John realized that he had been had. But as quickly as he initiated, Sherlock withdrew in disgust.

John laughed.

“Not a big fan of onions, are you?” he said, taking another bite of the abominable bulb. “Fuck,” he added loudly. His tongue burnt.

“Why are you _eating_ that?” Sherlock wanted to know, wiping away the sharp flavor from his own lips. “It is - it is _poison_ -”

“- It is not!” John swallowed, blinking tears out of his eyes.

“John,” whispered Sherlock gravely. His expression was suddenly like a child that had just borne witness to the death of a pet and was awaiting an adult’s wisdom.

“What is it? Don’t tell me that onions are _actually_ poisonous to the undine -” John asked with a watery sniff.

“What is _happening_ to you?” Sherlock wanted to know. “Are you dying?”

_Dying? What on earth is he going on about?_

John dropped the half-onion in the water and knelt that he might be closer to eye-level with Sherlock, who had slumped into repose in the surf. Sherlock’s hand came up as John drew near, cupping his face. His thumb swept slowly through the wet trail on John’s cheek. _Oh._

Sherlock did not seem familiar with the biological response of crying.

“Cor. No, Sherlock, I’m - I’m fine, it’s just weeping,” John started to lift his arm, intending to wipe away the tears, but Sherlock caught his wrist.

“What is weeping, then?” he rumbled.

John considered his response. For an Englishman, tears were considered inappropriate even at the most emotionally trying times.

“Well in this case the onion is to blame. It irritates the eyes.”

“Then do not eat them,” Sherlock said, frowning and looking somewhat distressed.

John felt a burst of tenderness and held up his hand to silence Sherlock.

“Goodness, no! You and the onions are not to be blamed, but my own impatience. I should cook them to lessen their spice. But Sherlock, I must tell you that a man doesn’t weep only because he has eaten an onion.”

“When, then, will a man weep?” Sherlock’s voice was icy. It was obvious that he did not appreciate his own dearth of knowledge on this topic.

“When he is deeply saddened, and when he experiences great loss.”

“Have you?” Sherlock rebounded with such speed and clarity that John was quite taken aback.

Startled by the bright keenness of Sherlock’s eyes, he fell quiet. Sherlock was watching the progress of a single water droplet as it followed the landscape of John’s face, coming to a quivering rest on the corner of his mouth.

“Have you?” Sherlock repeated, more softly.

John thought about his parents. “Yes, Sherlock. I have experienced great loss.”

“Ah. I have not,” Sherlock murmured, and suddenly he was in John’s space, ozone-cool breath like a thunderstorm.

With xenophilic curiosity, the undine licked away John’s tears. His gentleness made something tight unwind in John’s chest. He laughed to lighten the mood.

“I’m not presently distressed, my friend, merely afflicted by onion.”

Sherlock released him and picked up the offending bulb where it bobbed in the surf, spinning it for perusal in his webbed fingers.

“What strange creatures humans are.”

“I won’t tell you nay!” John said. Then, “Don’t eat that. It’s been in the ocean.”

Sherlock stared at him.

John realized how ludicrous his remark was, and snorted aloud. “Oh.”

“ _Oh_ ,” agreed Sherlock, shaking his head as though John were an amusing child.

He looked contemplatively at the onion.

“Don’t,” said John.

Sherlock sniffed it.

“You’ll regret it,” John warned him with a snicker.

Sherlock made eye contact. He bit into the onion. The expression he made and the speed with which he spat it out had John dissolving into fits of laughter; Sherlock whirled like a hissing cat and vanished into the waves with a colossal and punitive slap of his tail that drenched John.

But John’s good humor could not be washed away, for he had _vegetables_.

Shaking his wet hair like a dog, John jogged back up the beach and settled down to peruse the contents of the burlap sack more thoroughly. So engrossed in peeling and cooking did John become that a few hours vanished without his notice. It wasn’t until he was sitting on the beach that afternoon with the sun beginning its slow descent across the Maltese waters, that John realized Sherlock had not returned.

He had not forgotten the color change, or Sherlock’s reaction - he was curious about the Riptide. He did not know what to expect. Chewing and swallowing the last of the starchy Jerusalem artichoke (which he had had mashed into a kind of paste inside an old coconut shell), John wiped his fingers on his bare thighs.

“Sherlock?” he called out to the ocean.

He waited.

There was no response.

“Mm.” John squinted at the sky - he had an hour or so before the sun set. That was enough time.

He wanted to know what was going to happen to Sherlock. He desired to see, to know firsthand, what the mysterious Riptide entailed. It would be ungenerous of John to simply wait on the island. Perhaps Sherlock needed his help. What if Sherlock was at this very minute molested by mermaids in his grotto? It might be dangerous.

 _I should definitely check on him_ , John told himself.

John jogged to the northwest portion of the island, where in the distance he could see the stark black outcropping of rock that was Sherlock’s grotto. He couldn’t see the supernatural currents from his immediate location, but John figured that he had swum it once and he could swim it again. Besides, those supernatural currents hardly intimidated him anymore.

John knew firsthand that there were greater threats in the sea.

It was hard for John’s mind not to go to a dark place while swimming alone in the blue, for the experience with Olizarat would haunt his nightmares for the rest of his life. At least a current wasn’t capable of holding a personal vendetta against him.

So he waded into the deep until his toes could no longer touch the sand, and began to swim.

When he thought he had gone far out enough to evade the currents, John began the v-shaped swim inland. John cut through the water with steady, sensible strokes and glided into the shelter of the lagoon.

Perhaps Sherlock was not even in his grotto; perhaps he was out in the deep waters hunting. John stared up at the cavernous mouth of the sea cave, dotted as it was with brine and stalactites. The setting sun cast butter-colored highlights upon the dewy rocks. It was a rather impressively high-ceilinged rock formation, and the natural lighting here could not be more picturesque - quite fitting for a merman’s lair, John supposed.

“Sherlock?” John called.

There was a quiet splash inside.

“Sherlock, are you here, old boy? Look, I’ve got here on my own - and no encounters with a sea monster, your brother included!” chuckled John, planting his feet and wading toward the flat rock in the center of the cave. “I wanted to thank you for that crate of victuals. And don’t tell me that onions are actually poisonous to your people, I shan’t believe it.”

Sherlock appeared, slipping out of the water and arraying himself atop the flat rock with such efficiency that he quite startled John for his sudden manifestation, let alone the changes that had apparently transpired in the mere hours they had been apart.

John stared.

The barest blush of color that John had noticed in Sherlock’s aural fins on the beach had now deepened to translucent teal - but it was the least significant change. Although his scales remained black, the rest of Sherlock's body had changed color.

Starting near the speckled black-and-white base of Sherlock’s fluke, velvet blue transitioned in a buttery gradient to turquoise, which in turn faded into the white ruffled hem. Like sparse constellations, alabaster freckling scattered over Sherlock’s color-flushed plumage. It was evident that Sherlock _wanted_ John to look, for he held his tail in a great sweeping arc behind himself, with the satin curtains of his caudal fins flared out like a peacock’s fan.

His skin had affected a subtle change as well.

Now, when the light struck at a certain angle, Sherlock’s torso took on the iridescent sheen of a soap bubble. This ephemeral effect was observable only when the undine was in motion, for his skin seemed as it always had when he was still. Sherlock stared silently down at John, resplendent and looming.

It was an orchestrated performance for an audience of one. John’s jaw had gone slack. _But how has he changed so much? He did not mention this aspect of the Riptide, if that is indeed what this is. We have been apart for naught but a few hours._

Sherlock drank in John's reaction, determined it was favorable, and commenced preening like a girl whose figure had just been appreciated. He even tilted his head slowly to expose the long line of his throat and the soft pink demarcations of his gills.

At last John managed to say, “I thought - I thought you said you would be in the thick of it _tomorrow_.”

“I will be,” Sherlock replied, and his voice was soft and low. “This is but the beginning, little one.”

John didn’t know what to say, so he said nothing at all. His traitorous gaze strayed south.  Although the undine’s cockstand had yet to make an appearance, John was certain as the sun rises that Sherlock was aroused. The undine must have the ability to master their intimate anatomy in a way humans could not - and that was an enviable trick.

Sherlock’s genital vent was a tempting little slit of pale pink between his pelvic fins. It looked slightly swollen - John wanted to run his fingertips along that silken edge, to see if it was as soft as it looked. Cor, but it reminded him of a woman’s sex! Sherlock followed John’s gaze. He leaned on one hip and pressed his fingers over his own entrance, spreading his first and middle fingers in a V, which he scissored open gently in order to make a lewd display of the pinkness within.

John flushed and looked away. Sherlock was shameless in his sexuality.

“You should go, mine own. Go back to your own dry land.”

“Why should I go?”

“Because if you stay, I will not be able to keep mine own promise that I will not harm you, or forcibly keep you in mine own nest,” replied Sherlock, and his voice had a rote quality to it that informed John that the undine remembered with crystal clarity the exact terms of their agreement.

“I would rather stay," John murmured.

“John Watson, you do not _understand_. Soon mine own perfect mind will be clouded by lust, besieged by carnal desire to rut and mount and _fuck_ ." Sherlock clipped the fricative with the precision of a jeweler cutting a fine gem.  It was filthy. It was glorious. "I shall not wish for you to leave mine own sight, and I shall not stand for it if you leave me.”

Some part of John resented the merman for trying to protect him, and some part of him did not want to miss a moment of the Riptide, this unique example of undine biology. John could not say with any certainty whether it was the former or the latter that motivated the perversion of his reply:

“If you want me to leave, you must claim the favor I owe you. Otherwise I will be staying right where I please, which, presently, is right where I am.”

Sherlock raised his eyebrows. He slithered into the water without a sound. His gleaming peacock-colored fluke slashed above the other side of the flat rock, obscured to John.

The sun had succumbed to the dusky lavender of twilight, revealed as it was through the hole in the grotto ceiling. John waded toward the rock. He was drawn to the potential for danger. He wanted to rub himself up against something frightening, something larger than himself. Only in the presence of something dangerous did John feel alive.

“It seems to me that my presence hinders your natural preferences during this time. I do not understand what the Riptide is, or what is expected of one during it  - but I would not like to wait out this time on the island without you, wondering if I - if I might have been your Riptide lover.”

A deep chuckle reverberated in the wet echo chamber. A heavy presence manifested at John’s back. He whirled. Sherlock was mostly submerged. To the cursory glance he was more sea serpent than man. His eyes glittered like sunken silver.

John’s heart rate skyrocketed and he reached reflexively for his knife.

Sherlock struck like lightning, erupting half out of the water with a tumultuous shove of his fluke. John found his arms snatched tight to his sides with crushing force; one moment, he had been standing in the shallows of the grotto, the next saw him pinned with merciless force against the flat rock.

John’s shout was belated.

The undine pressed his face against John’s lower abdomen underwater, mouthing at the tender skin there until John felt the icicle-prickle of teeth. John clapped his hands on Sherlock’s shoulders. He was a strong man, but there was no way a human could best Sherlock for strength. For a moment John was afraid that Sherlock would open his mouth wide and bite into his flesh, yank with his jaw and teeth until John’s internal organs poured out in a ropey mass of red and white. But this nightmarish notion was not made truth; Sherlock softened his mouth and bestowed tender kisses down, down, down.

The barrier of John’s kilt was torn away, and John flinched as hooked claws scraped his hipbones. There was a brief, tenuous moment of peace. John swallowed. He was semi-erect despite his fear, or perhaps because of it.

Sherlock’s hair was a transient cloud in the current where John looked down upon him; the strong white line of his back melted into the black of his scalier anatomy. His tail was partially obfuscated by the satiny, colorful curtains of his drifting fins.

He stood out in stark contrast to the sugar-colored seabed.

He stood out in sharp contrast to any lover John had ever known.

“You’re incredible,” John whispered.

Sherlock heard him. The undine’s head sleeked out of the water, his gills flared out like a lace collar. His eyes were bright, lustful and full of wonderment. “You’re _aroused_.”

“It is a state with which I am becoming familiar,” John said gravely.

This startled a laugh out of Sherlock. John grinned back, and felt his pulse race as Sherlock lifted him up and out of the water with ease. The novelty of being thrown about willy-nilly usurped John’s indignation. He found himself further placated by the liberal application of velvet lips to the throbbing underside of his cockstand.

John groaned, scrabbling for purchase on the now-damp rock. Sherlock cradled the thick vein on the underside of his cock, curling his tongue into a soft wet channel which he drew languidly up, up, up that hot length until he could seal his lips over the crown. Watching his cock disappear into Sherlock’s mouth was thrilling; John dropped his head and groaned.

Sherlock opened his throat to the intrusion, sliding his beautiful face down until John was quite enveloped in warmth and slick, hugging pressure.

“ _Fuck_ -!” John whispered.

Sherlock withdrew with a wet slurp that somehow managed to sound self-satisfied. Most of the blood in his body had migrated to his groin. He trembled and focused on his breathing. He did not want to spend like a green lad mere moments into what was evidently shaping up to be an afternoon of carnal novelty.

Sherlock took him by the hips and flipped him over the rock. Bent over like this, John’s undercarriage was quite exposed. The position was terrifying for he could not see Sherlock’s face or deduce his intent; what little communication was left vanished.

“Sherlock!?” cried John, distressed.

"Shhhhh," crooned Sherlock.

Wet hands caressed John's lumbar dip, but John was not sufficiently gentled. He had half a mind to pull himself away, to reorient his body that he might face his capricious lover, but Sherlock felt his muscles tense and then there were claws needling his hips. A sibilant noise of warning; a cool nose brushed the curve of his arse.

Sherlock tested the firm muscle of John's buttock with the points of his teeth. “Mine own. Brave little human, come straight to mine own nest. You want me, you need me - John, say that you need me as much as I nee-”

Sherlock stopped, seeming to remember himself - or at least the version of himself he wanted John to see. He nipped John's arse again in misapplied reprimand. John grunted, but was busy trying to regain control of his breathing. He dropped his head to his forearms and spread his thighs. Sherlock immediately palmed his rump, opening John’s body to his perusal with his thumbs.

“Sh-Sherlock,” John said, cursing the breathiness of his voice.

Sherlock licked a hot stripe from John’s bollocks, up the root of his cock and over the tight pink furl of muscle that marked John’s most intimate of spaces. It was a deliberate and primal touch; a thrillingly curious investigation provoked, no doubt, by the novelty of human undercarriage to the undine.

John was not unfamiliar with the delights of this particular portion of his own anatomy. The hairs on the back of his neck prickled in anticipation.

Sherlock’s tongue stroked again and again over that hot bud until John quivered and moaned like a halfpenny whore, self-conscious of the noises he was making but unable to temper them. Frissons of pleasure sparkled up John’s spine. His legs went to jelly and big webbed hands squeezed his arse cheeks, supporting his weight - but then the undine drew back.

John panted.

He twisted his head around in an effort to see what was going on behind him, but it seemed Sherlock was only examining his arse with that characteristic mix of scientific curiosity and sexual arousal. John canted his hips back in wordless request.

There was a baritone chuckle and John flinched at the gust of breath on his relaxing arsehole. Sherlock glided his tongue up and down the interstice, spreading John’s cheeks that he might bury his face between. His tongue passed over the puckered skin and then stiffened into a delicate point which he slipped into the recalcitrant little ring of muscle.

John buried his face in his arms.

“O-Oh, _Sherlock_ -!”

That inquisitive tongue speared inside, abstemiously at first, but with increasing pressure as John’s muffled cries of delight encouraged him. Sherlock was moaning low in his throat, deep keening sounds of such profound longing that John found himself muffling his own pleasured grunts that he might hear better. Sherlock’s tongue caressed the underside of his bollocks, heavy and full, and fluttered against the root of his cockstand. Cool fingertips ghosted over John’s cock where it lay flush and pointing down along his thighs, bent as he was over the rock.

Then Sherlock was possessed of some predatory freak, and he withdrew only to ascend onto the rock behind John, pelvic fins clapping tight to John’s hips and palms on either side of John’s shoulders. He supported his weight with a palm next to John’s shoulder, the other hand lifting John’s hips clear off the rock until his black-scaled hips were flush against his arse.

Water dripped from him onto John’s naked back.

 _I am a fool not to be frightened_ , thought John, for the strength in the body lying atop him was breathtaking, the obvious restraint in the slow rock of Sherlock’s hips arousing and alarming in equal measure. Was there ever a man in history who had known an undine before? What man would permit a _merman_ to mount him?

One who had lost his mind, perhaps.

John wasn’t sure if he was prepared to play catamite to a monstrous merman, but Sherlock made up his mind for them by sliding the distended weight of his cock between John’s thighs. That inhuman cock pressed John’s erection against his own belly, dragging luxuriously back and forth, and back and forth, spreading slickness.

Both of them were panting with need, crushing their hips against each other in asynchronous desperation. Sherlock dropped his head down and black curls tickled John’s cheek. He turned and their lips met despite the awkward position, and John could feel the fat weight of Sherlock’s cock laying in the valley of his arse.

“John,” whispered Sherlock, voice broken. “Oh, _John_ , can I? I must - I _must_ -”

“Yes,” growled John.

The fluted crown nudged against John’s arse and John, god help him, invited him in. He took it, and it burned in that odd-but-familiar way, and he took it some more, as inch by throbbing inch that coral length disappeared into his body. It was pain and satisfaction - particularly the latter- and John grit his teeth and bore it, grateful in turns for Sherlock’s curious tongue and natural lubrication.

Sherlock went slowly, but he did not stop, even when John’s back muscles spasmed. John swatted the undine’s hip. Sherlock rumbled an amused noise directly into John’s ear but did not stop. John dug his fingernails into Sherlock’s forearms where they folded over his neck and chest, hard enough to draw blood. John only felt the slick steel inside of him pulse excitedly in response. He growled and tossed his head, thighs spread as far as they would and trembling with the effort of willful bodily submission.

“ _Ah,_ it is a cruel organ..!” John growled lowly, voice strangled with discomfort.

“Take it,” whispered Sherlock softly, sucking the lobe of John’s ear into his mouth and gently pinching it between his teeth. “Oh, John, _please_.”

John heard that velvet baritone rumble through his spine where Sherlock’s narrow chest pressed into his back, and knew that he was lost. He would do a great deal to hear Sherlock say his name like that again. He would follow that voice to the bottom of the sea.

Sherlock shuddered with arousal. He mouthed softly at the exposed nape of John’s neck.

In that moment, John was not thinking of his predicament, or of London, or of the dangers of a life on an untamed island. He was aware only of the glisten of saltwater on Sherlock’s forearm, the copper-sweet blood on his tongue, and the searing pressure inside him.

Sherlock could break his neck from this position. He could turn John’s back to bloodied ribbons with his talons. He could drag John over the edge and drown him. John could not buck him off, could not escape. The danger could not be ignored, and John had never been so aroused in his life. He felt the cool press of scales against his arse.

Sherlock sighed in bliss. The undine was nuzzling the nape of John’s neck adoringly, mouthing the skin there and scraping sharp teeth over the knobby bone. He was not moving, just… holding himself inside as they both adjusted. John could feel Sherlock's heartbeat in his arse.

He willed his muscles to relax, pliant and receptive to the possibility of pleasure. His body remembered lovers past, recalled the sweet reward for patience in reception; the burn would transform to heady pleasure if he let it. If Sherlock would _move_. He wanted Sherlock to move. He wanted the undine to fuck him, wanted Sherlock to use his body to sate the base urges that were consuming him.

“Go on then,” John said, voice coming out rather stronger than he had expected it might given the circumstances.

“Mine own…”  Sherlock’s voice rumbled from above, barely distinguishable as English.

He curled his body over John and began to slowly piston in and out. The tow of his heavy cock produced soft, wet noises that coaxed the flush from John’s throat up and into his face. The care with which the undine now favored him was infuriating. John’s loins were afire, his heart a thunderstorm, his breath a thousand tiny hurricane gales.

Suddenly furious, John barked: “I - am - not - _glass_ , Sherlock! Y-You say I am yours. Well! If that is so, you have me now; _so take me_ -!”  

This was not the time for gentle lovemaking. John bucked his hips back, inhaling at the sensation of the soft fleshy barbs at the base of Sherlock’s penis pressing into the soft skin around his access.

This challenge affected Sherlock profoundly, for he hissed aloud and took a moment to adjust himself with both palms on either side of John’s trunk. The sudden punishing slap of his hips provoked a deep shout from John. And once he started, Sherlock almost instantly found his rhythm. God, but Sherlock fucked like he was _made_ for it; snapping, perfect rolls of his hips unhindered by the pecularities of his mythological anatomy.

John was quite overcome. His cock was rather in danger of becoming sandwiched between his belly and the rock surface as Sherlock’s weight gradually pressed John down and forward, the vigor of their coupling sending him skidding forward with every thrust.

“John.” Sherlock’s voice rumbled from above. “John, don’t tell me to stop, oh! Tell me it’s all right, say that you are mine - please, please -”

“It’s all right,” gasped John, because it was, and then: “I’m yours.”

“Yes, mine own little human - so strong, so warm inside,” Sherlock’s voice was reverent, the tone of a new believer. “So, so hot, ahnnn..!”

John choked out a surprised laugh. _You're an easy one to impress_ , he thought affectionately, and he squeezed his muscles in a slow milking motion, which caused Sherlock to gasp brokenly and bury his chin in the hollow of John’s clavicle. John trembled with the effort not to spend.

“John, John, _John, oh.”_ Sherlock’s voice was so deep it barely registered as discernible English.

“Mmm, yeah, that’s it,” growled John, reaching behind himself to grip the base of Sherlock’s pelvic fin where it coveted his iliac crest. “S-So big -”

“ _Yes_ ,” purred Sherlock in vain agreement, as attuned to the possibility of flattery as a hawk is to the presence of a hare.

John had never felt so claimed in all his life. Sherlock’s thrusts became powerful enough to scoot him yelping forward along the length of the rock and a huge webbed palm pushed him firmly down, pinning him in place as the metronome of Sherlock’s hips slapped his arse again and again and again until John was reduced to the incoherent glossolalia of carnal pleasure. Sherlock’s thrusts sped and the soft barbs that had been slipping easily into John’s body with each penetration now stiffened somewhat, transforming the experience of being fucked into something more raw.

Sherlock mouthed frantically at the crux of John’s shoulder, little faux-bites that made John want to shout ‘ _do it already!’_. John’s erection hadn’t flagged in the slightest. He shoved his hand underneath his belly to reach for his begging cockstand. But Sherlock’s hand snatched his arm and twisted it behind his back.

“No,” he forbade John, breathless, and John _snarled_ and bore down furiously on the slick steel inside of him, yanking on the pelvic fin that was still in his grip. Apparently this roughness was not unwelcome, for Sherlock shuddered deeply and spent. He bit John sharply on the shoulder.

It was too much sensation, the pain of the bite and fullness of penetration catapulting John over the edge: he fell into the abyss of his own paroxysm, frightful in its intensity. His untouched cock twitched against his belly, striping the rock below with white. For a moment John felt like a spirit, floating above his own body as voyeur to this brutish coupling. 

He took great heaving sobs of briny sea air. _What have I done?_ John thought for an instant, and only because the pain in his shoulder was no trifling matter. He could feel blood trickling down where it followed the line of the hemp rope about his neck, down the white curve of Olizarat’s tooth where it lay on the rock.

John felt raw. He felt raw _everywhere_ , not just the most obvious of places, and he suddenly wanted for nothing more than a clean deep breath of air. Sherlock was heavy upon his back, collapsed forward and panting, nuzzling his face into the bite mark he had made. It was obvious that the undine had no intention of moving, his enormous member still inside John with no appreciable decrease in tumescence.

“Off,” gasped John. “Off, off, _off_ blast you!”

Sherlock stiffened. He stopped stroking his face into the bloodied mess of John’s shoulder and lifted himself up and away, removing himself from the hug of John’s body with broadcast reluctance. The splatter of _liquid_ , of _spend_ , into the ocean below was suddenly embarrassing to John. He drew his thighs together self-consciously even as Sherlock dismounted. He dragged his face adoringly down the length of John’s back - pausing for an overlong perusal of John’s undercarriage as he went.

Irritated, John swatted at Sherlock with his foot, catching the merman in the shoulder and shoving him back.

Then he rolled onto his back and sat up with a flinch, clutching the bite on his shoulder as though pressure alone could alleviate the pain. His arse _burned_ , and he felt strange and full.

Sherlock looked up at him guilelessly from the water of the grotto. The beautiful satin curtains of his fins swirled around him. They may have looked as fine as a butterfly’s wings, but John knew firsthand of their resilience. He looked radiant, aglow with a healthy energy and the most self-pleased expression John had ever seen on any living creature.

Irritated, John searched Sherlock’s face for any evidence of shame.

There was none.

Not even a _hint_ of guilt for his roughness, for biting him. If anything, the undine’s expression of immense self-satisfaction was transforming slowly into something that John might have called concern on any other man.

“Mine own…?” whispered Sherlock, voice impossibly soft and patient.

“No. Don’t you _mine own_ me, Sherlock.”

Sherlock fell silent. It was obvious he was trying to work out what he had done wrong. He swam closer, warily, pushing his head close to John’s bent knee on the edge of the rock. Sherlock glanced up at him, beseechingly, and his lips were stained with blood.

_See how he looks at me, with his teeth red with my lifeblood. Would he have done this with any human he comes across, any man who could survive his fickleness? Was it the Riptide that made him behave thus, or genuine desire for me?_

But then John noticed Sherlock’s adipose fin.

It trailed out in two ribbons that had once been whole, bisected by the monster Olizarat. Sherlock's fin had been ruined in defense of him. It was a scar that the undine would carry for the rest of his life. If that wasn't an expression of regard, John would eat his hat.

John’s anger melted away. He dropped his hand apologetically into wet black curls and was grateful when Sherlock butted up into the touch like a cat.

Congress with Sherlock had been a confusing muddle of pain and pleasure. It was underlaid with a bone-deep satisfaction and a sense of rightness. That, more than the pain or pleasure, was what confused John the most. Sherlock was not human. To expect a coupling of this nature to be akin to a human coupling was unrealistic.

Sherlock was rumbling out a subsonic Song under his breath again, a low vibrato that suffused his body with contentment.

“No more biting," John said.

"Little bite," murmured Sherlock, twisting up to suck John's fingertips into his soft mouth. He fellated them briefly, gazing directly into John's eyes. John felt a distinct pulse in his own sleeping cock.

"No."

Sherlock released John's fingers, trailing his plush lips over the sensitive tips.

"You bit me, mine own," Sherlock bartered, presenting his forearm with a flourish. John saw that he had broken skin on Sherlock's slender forearm. The merman looked pleased.

"So I did," John replied. "It dawns on me this must be a habit of your people."

"It is so," admitted Sherlock. "I wish to hold you now."

John’s heart skipped a beat. He had been half afraid that Sherlock would vanish into the ocean after their congress. The revelation that the merman craved intimacy with him was flattering. He must have been silent for long enough to distress Sherlock.

“Please, John. I - I cannot, I must. It aches, mine own little human. You cannot possibly imagine how much it _aches._ Stay with me _._ ”

Sherlock reached up his wet arms and John slid off the edge of the rock and into the water with him. The cool ocean was a sweet balm on his sore body, and he groaned in relief, chuckling when Sherlock skidded their cheeks together and rubbed. It was evident he appreciated the texture of John's whiskers on his own scaled cheeks.

"Will you stay?" Sherlock repeated, his breath tickling the wet gold bristles of John's beard.

"For the Riptide?"

"Yes."

"That depends on whether you intend to leave me intact by the end of the experience, love," chuckled John.

Sherlock froze.

John tried to draw back to look at his face. He wondered what the undine was thinking. But then Sherlock was pulling him into the serpentine coil of his tail, rolling John in the fabric of his fins right there in the water in a full body embrace no human had the anatomy to replicate.

"I will care for you, mine own. You want me -" here John snickered at the assuredness of his tone - "and I want you, I want you more than I have ever wanted anything in mine own life. Say that you will be mine own Riptide lover, let me learn all the ways to make your own body sing its pleasure."

John's throat was dry and his cock was proud again. Already.

"How could I say anything but yes?" John breathed, and he took Sherlock's marvelous face between his palms and kissed him.

 

**Notes for the Chapter:**

> Wow. I couldn't have predicted the buzz that Riptide Lover has inspired in the Sherlockian creative community; piles of [beautiful artwork](http://jinglebellfic.tumblr.com/tagged/gift%20art) and even _dolls_ are being made. Talk about talented! You can check out folks' stellar creativity in the [#riptide lover](http://jinglebellfic.tumblr.com/tagged/riptide-lover) tag on my blog, as well as peruse reader comments, questions, and song recommendations. The playlist [is here](http://8tracks.com/jinglebell-fic/riptide-lover).
> 
> In addition to that, I've sketched up a few things for illustrating various chapters. Check out Chapter 8 for [a sketch of Sherlock on the beach](http://jinglebellfic.tumblr.com/post/110490617121/i-felt-like-sketching-undine-sherlock-from-my-fic), and the sketch of John ~~'s bubble butt~~ , [do you lift or something](http://jinglebellfic.tumblr.com/post/110230483786/been-home-sick-most-of-today-and-toward-the-end)? 
> 
> The next update is a direct continuation of this one, but I'm still working on it. I'd like for it to be posted before the end of the month. As always, you can find update info on the blog!


	14. Riptide Lover [Part II]

**Notes for the Chapter:**

> This chapter is a direct continuation of the previous one. My hope was to update before the end of February, but that was a bit of an unattainable goal. Thanks to Red and JP for beta'ing! Review the tags and be a responsible reader, THANK YOU! Cheers! Also... ~sparkles loudly at Anarfea~
> 
>  **ALSO:** I will be at [221b Con](http://221bcon.com/) in April. Upon request, I am doing a (very!) informal Q&A for Riptide Lover. I haven't picked a time and place for that yet. Those of you who might be at the convention and are interested in geeking out about merlock things, keep an eye on my blog for more info!
> 
> Without further ado.

****The next morning, Sherlock's first caller came soliciting for his attention. The mermaid's Song floated in on the wind from the sea. It was high pitched and eerie, a wail that sounded lonely to John’s ears.

John sat up on the flat rock.

Sherlock himself looked unconcerned, merely perking up at John's sudden activity and gliding over. He had been floating in the entrance of the grotto, staring out at the sea in mute contemplation. His huge hand settled on John’s thigh. His thumb pressed soft circles into the skin there.

"Will you go to her?" John blurted.

Sherlock raised his eyebrows.

"That is - that is, I must confess I have no desire to be eaten this night. You yourself said that your kind do not take kindly to humans."

Sherlock paused for a long moment, assessing John with those icicle-clear eyes, and then finally replied, "I do not desire her company at present."

"Well. Will she come here?" John pressed.

"It is mortal offense to enter another's territory uninvited during the Riptide," Sherlock said, glancing out across the sea as though searching for a trespasser. “She will eventually deduce that her seduction falls on unsympathetic ears. She will tire of the effort and move onto her next conquest. There are plenty of males for her in the sea, John."

John sat on the edge of the rock and let his feet dangle in the water. Apparently this was interpreted as a seductive effort by Sherlock, who rumbled appreciatively and moved his hand over John’s calf. Watching to make sure he was agreeable, Sherlock took John's foot in hand. John had small, neat feet - a Greek foot, with the second toe longer than the first.

John was somewhat distracted from thoughts of murderous mermaids. He curled his toes down and pinched the side of Sherlock’s hand.

A slow, pointy-toothed smile spread across Sherlock’s face. John felt something in his belly go molten with a feeling much more dangerous than simple lust. Sherlock sunk in the water in order to mouth at the ball of John’s foot, smoothing his lips over the skin in a slow, open-mouthed kiss. John watched in awe as Sherlock so obviously took pleasure in rubbing his cheek against the thin skin of John’s arch.

The undine began to rock his hips in the water. John caught a glimpse of vif coral below: evidently Sherlock's interest transcended scientific curiosity. Sherlock took John’s toe between his lips and sucked, a light pull that shouldn’t have had any effect on John at all - except it did. It sent the phantom sensation of his lover's lips straight to his cock.

John gasped, opening his thighs somewhat to accommodate his thickening cock. Sherlock glanced up with bright eyes, gaze lingering on the furious red bite mark above the ravage of John's bullet scar.

“Touch yourself,” demanded Sherlock.

He licked his lips pointedly at John’s growing interest.

“Don’t mind if I do,” John replied cheekily.

He gripped his cock and pulled slowly to the head, a barely-there pressure that made him want to rock his hips up, up into the deliberately unsatisfying curl of his fingers.

Pleased, Sherlock occupied himself once more. He took a second toe into his mouth and groaned aloud, eyes fluttering closed rapturously. He pulled free with a wet pop in order to skate his cheekbones against John's calves, like a cat bestowing its favor. His caudal fins slashed out of the water behind him.

"Sherlock, come here," John said, grinding the heel of his palm slowly into the base of his own erection.

The undine, who was currently repeating the ritual on John's right foot, grunted his disinclination.

"Sherlock," insisted John. He was hesitant to lift his foot away lest he be nipped. "Come on then, there’s a good lad."

Even with toes between his lips, Sherlock managed to look disdainful. Time to try a different tactic. John flashed a mischievous smile. It was the same smile that had won him many a lover. Apparently even Sherlock was not immune, for he released the much-coveted toe and drifted onto his back.

His pelvic fins were thrown open in whoreish invitation. His penis curved elegantly up against his belly, twitching almost imperceptibly with the beat of his pulse and gleaming with slick fluid. John's arse twinged at the recent memory - it was so very large.

 _Let it not be said that I am an uncreative lover,_ thought John. He used his feet to stroke both sides of Sherlock's cock simultaneously, pulling up along the length. Sherlock momentarily forgot to tread water and sunk a few inches, which made John's smile turn wicked with triumph. He reversed the stroke, sliding his feet down until he felt the ring of soft barbs at the base of Sherlock's penis flex into the pressure of his soles.

Sherlock tossed his head in helpless arousal, staring up at John from his mattress of waves.

 _"_ I don't think you enjoy this very much," teased John, voice mild as if they were having a discussion about the weather.

He pressed Sherlock’s cock down against his belly with one foot and used the other to rub the head, spreading his toes and pushing them lightly into the firm pink flesh.

Sherlock made a broken sound. It was beautiful.

"Oh, what's that? 'Stop'?" John asked. He made as if to take his foot away.

Sherlock rumbled furiously. Chuckling, John took pity on him and reapplied his much-appreciated feet.

"Go on then. I want to feel you spend all over my feet, gorgeous."

Sherlock apparently agreed, for the rocking of his hips increased in tempo and he gripped John's thigh for balance. After only a few more moments of this, the undine spent.

Sherlock was beautiful in the throes of his paroxysm, and now that John could see his face he appreciated it all the more. Sherlock's brow furrowed and his mouth dropped open, a silent cry. He looked overcome. Warmth flooded John’s feet, pulsing hotly over the arches and dribbling between his toes.

“That’s it,” John heard himself growling, shocked at the ferocity of his own tone. “Come for me, there's a boy."

Sherlock shuddered a final time, and the evidence of his pleasure was swept away by the adroit pendulum of the waves. His chest was heaving. If he were human, he would be flushed from head to toe.

John kept one foot planted on Sherlock's hip and moved the other up his narrow chest. He ignored the throb of his own arousal in favor of basking in the triumph of having brought Sherlock to this post-orgasmic lassitude.

Sherlock caught up his foot and kissed the inner arch.

"John."

"Mm. Yeah?"

Sherlock floated in the decadent, jewel-toned piles of his own plumage. He sighed with inexpressible contentment.

And John couldn't seem to stop smiling.

~  ~

For a few hours, Sherlock was content to swim in a circle around the flat rock. His breathing was shallow, and he often affixed John with a piercing stare. His dorsal fin, which usually lay sleek against the curve of his rump, was fully extended in a way it heretofore had not been. It made him look larger than he really was.

John lay with his arms pillowing his head and observed his strange lover. He was still sore from their earlier coupling, but it was a well-missed ache. The quiet susurrus of Sherlock’s fins slicing through the placid wavelets eventually lulled John into a doze.

He woke a few hours later to the sensation of water dripping onto his face.

The source of the drip was Sherlock’s wet curls, where he bent over John on the rock. Something long and thick was laying against John's hip. It took him a moment of groggy reflection to realize that it was Sherlock’s erect cock.

"Mine own," acknowledged a familiar chocolate baritone. Taloned fingers traced John's scar.

“Again?” mumbled John, unable to smother his smile. The afternoon sun gave Sherlock a halo.

He gripped the base of Sherlock’s cock and gave it a sleepy pull all the way to the delicate, fluted crown. The proprietariness of this gesture seemed to drive Sherlock wild. His eyes were bright when he leaned down for a kiss. John reciprocated, and soon they were tangled in each other's arms.

Sherlock’s tail was looped in a heavy semicircle around John on the rock. His fins spilled over the edge and floated on the waves.

As their tongues curled lazily together, John drifted his hand down to stroke Sherlock’s plumage. His fingers lingered over the bisected adipose fin. The color brought to mind some distant genetic memory, a vague image of lush green forests and placid blue lakes. He brought the sash-like skin to his lips and kissed it. Sherlock tasted like a stormcloud.

In the water, Sherlock’s fins looked gossamer-fine, as though spun from cobwebs. But these fins were rubbery to the touch. They were much hardier than they looked. Inspired, John sat up and sunk his fingers into the fabric of the undine’s caudal fins. He tugged. Sherlock gasped aloud - and John _loved_ that gasp, loved the breathy quality of it.

He wanted to hear it again.

John scooped up overflowing handfuls of that jewel-toned plumage and pulled until Sherlock quivered, keened, and opened his pelvic fins to display himself. The invitation could not have been clearer.

“Ah-ha! I do believe I have found your weakness,” crowed John.

John straddled him, blood hot. He reached behind himself and without preamble sunk a finger to the second knuckle inside his own body. He was still slack and tender from their previous coupling.

Sherlock’s eyes went wide and bright, staring unabashedly at the place where John penetrated himself. Long, webbed fingers kneaded the muscles of John's thighs in greedy anticipation.

“Here is how we shall proceed,” John husked, sliding a second digit in alongside the first. “If you want me to last this Riptide with you, you must do as I say. And this time I should like for you to go slow and be a gentleman, for that's what I'm presently in the mood for. Can you do that?"

Sherlock made as if to reply, but John arranged himself at the tip of Sherlock's hard cock and sat down upon it, and in doing so rendered Sherlock quite speechless. John breathed through the deep stretch and took his time. No human lover possessed the anatomy to fill him so completely, and he reveled in the unique sensation.

His arse met fine, black scales.

John watched Sherlock's eyes close, wet black lashes casting faint shadows on the prominence of his cheekbones. He was such an ethereal beauty - how many sailors had Sherlock lured to their death before John?

It didn't matter.

Sherlock was his now.

The muscle burn as John lifted his hips trickled like slow-moving lava up his spine. He enjoyed every minute of it. The nearness of Sherlock, the tickle of clawed fingertips, the insistent press of pelvic fins, and the heavy pressure of him inside sent John fully into the realm of the physical, incapable of higher thought.

There was nothing before or beyond this moment.

John rode Sherlock with slow, maddening little swirls of his hips, setting a rhythm with shallow pulses. His arse was slick and receptive, and he took perverse pleasure in the ease with which he opened to the intrusion, and the silken burn of it. _God, yes_. John leaned on the heaving line of Sherlock's breastbone as he moved, tossing back his head.

"Yes, oh, oh, _oh_ -!"

John lost himself in sensation, taking the stimulation he desired. His cock bobbed against his belly and he took the tip between his fingers and edged under the glossy head, a barely-there pressure that drove him wild. He was aware that he was making sounds, sounds a whore would blush to hear, but he could not be arsed to care.

John’s pace was as unhurried as his language was desperate.

"Sherlock, g-god, yes..! Oh, _fuck_ , oh, you are s-so big -"

Sherlock whined. He rocked his hips up, and John winced - he wasn’t ready to take all of it yet.

"No," murmured John. "Stay still, love. S-stay still for me, there's a good lad."

Sherlock made a frustrated sound, but his pelvic fins gentled where they cupped the curves of John's arse in mute acquiescence. It was in this way that John chased completion, bouncing on Sherlock's inhuman cock: when he spent it was was drawn from him slowly and leisurely, decadent pulses of pleasure that painted Sherlock's belly with spunk.

Sherlock trembled and quivered below John, staring with wide, seaglass-colored eyes.

"John,  _John_ -!"

"Yes, you’re so _good_ ," sighed John. "Such a wonderful thing you are, so beautiful, such a restrained gentleman when you want to be. Do you want to spend inside me, pet? I’d like that.” Then a wild inspiration took John. “I want you to fill me up.”

Sherlock broke into a long, wonderful low moan that heralded the arrival of his paroxysm. He cried out and writhed and John smiled down at the undine and rode him through it. He watched as Sherlock’s jaw slackened, eyes falling shut in the throes of pleasure.

Warmth blossomed inside of him.

"There," John sighed, leaning down as Sherlock reached up to enfold him in the damp circle of his arms. "Mm, yes."

~  ~

That second night, Sherlock left in order to acquire sustenance for John. The undine seemed to derive pleasure of a different sort in watching John consume the food he brought - but the lull didn’t last long. John had barely finished the second coconut before Sherlock was insinuating himself into John’s space, rumbling and purring and rubbing.

They ended up fucking again.

After this, John was so sore that he took refuge on the fifth level of the ziggurat steps, physically distancing himself from the insatiable creature in order to give his body some time to rest. His arse burned and he oscillated between feeling sated and cranky. Perhaps if Sherlock's spunk wasn't perpetually slickening the back of his thighs he would feel less irritable.

John peeked over the lip of stone.

Sherlock circled restlessly below, splashing as though by throwing a great aquatic strop he could somehow seduce John back into his arms for another go. John wasn’t sure how Sherlock knew that he was being watched, but the undine turned his sleek black head and met John’s startled gaze before John could duck back over the edge of the rock.

Feeling childish for having been caught, John stoically stared back. Sherlock’s mouth curved slowly into a pointed-tooth smile. He rolled onto his back, spreading himself open like a butterfly specimen floating on the water. His fins were blushing emerald and satin-blue, with starbursts of white.

"Mine own. I am here. Come down to me," crooned Sherlock.

His syrupy baritone reverberated with an overtone hum, a sound that promised unearthly pleasure if John would just stop being stubborn and go to him. John was strong. He could take it. His body would heal. He could take anything Sherlock would give him, he was grateful for it. Sherlock was his protector, his lover, his own. Why was John depriving him?

When John thought about it from Sherlock’s perspective, it was really rather cruel of him to withhold sex. _See how he suffers_ , John thought sympathetically. _He needs me, needs mine own touch_.

John blinked.

Something rang false there, something sounded off.

He grimaced, putting his hands on his temples. What the hell? Anger lent clarity to John’s mind, and he realized that Sherlock was Singing - albeit so faintly that it wasn’t audible to his human ears. _Damnit. He’s manipulating me again._ John couldn’t believe the nerve of him! But once he had isolated the source of his thoughts, John did not find it so difficult to shake Sherlock’s influence.

He collected himself, and then said matter-of-factly: "No. I think I shall rest here awhile.”

It took all of John's self-control not to laugh at the put-out expression with which he was now favored. It reminded him of when Sherlock tasted onion.

"John. John, _no_ ,” Sherlock said.

"Mm... S’quite comfortable up here. If I sleep down there, I wager you will wake to bugger me in the night and there will be nothing left of me for tomorrow."

There was a surly silence. The silence said, ‘that might be technically correct, John, but just give me a moment to conspire of some other means to get my way’. This took about thirty seconds, then there was a splash from below.

“John...” Sherlock’s voice was throaty, dropped into its post-sex register deliberately. “I need it...”

“You just had it,” John pointed out, yawning and rolling onto his back to stare through the hole in the cave roof. He could see the glittering carpet of the night sky.

It was a beautiful night out, the temperature just right and the moon a perfect thumbnail sliver. Sherlock blew angry bubbles. John burst into laughter at the incongruous sound, although he rather wanted to be annoyed.

"Sherlock! Goodness. Surely you must rest."

"I must _fuck_ you."

"Charming."

" _John_!"

"Shhh. I will come down tomorrow." John made a show of nestling down, rustling the pile of Algernon Portnay Kirk’s clothing (which he had balled into a makeshift pillow). The rocks on the ziggurat steps were even less comfortable than the flat rock, but here he would remain unmolested.

Sherlock splashed irritably below. John did not care. He was used to sleeping on a frigate with countless other bodies snoring, flatulating, and grunting nearby. Sherlock’s tantrum would not keep John awake.

~  ~

The next morning promised a day so dry it seemed the very air was crackling.

John woke and went for a swim out in the lagoon. Sherlock was nowhere to be seen, but that was not atypical; he often brought John food and water early in the day. The sun was bright and high already, with a pleasant cool breeze that John inhaled of deeply and held in his lungs for as long as possible, not wishing to release the sensation of freedom.

A quiet splash drew his attention.

Sherlock’s dorsal fin sliced through the waves. He swam into the lagoon and coasted up onto the fine gravel shoal near John. He disposed himself there like some rare porcelain sculpture, gills sealed to prevent gravel from getting inside.

The huge curtain of Sherlock's blue-and-green caudal fins rippled in the wavelets. The single white scale near the ribbons of his adipose fin gleamed like a beauty mark as Sherlock regarded him coolly.

“Good morning,” John said.

Sherlock said nothing, expression impassive.

John noted the wild squiggle of Sherlock’s pupils and approached with caution, wading into the swaying mass of Sherlock’s plumage. He saw the gills of Sherlock’s neck flex open slightly, the only physical indication that he was feeling John’s touch.

“Where were you this morning, hm? Off exploring again?”

John smiled winningly. It was the same smile that, in the past, had been rewarded with sex. To help it along, he deliberately shifted his stance where he stood in the water, in order to bring attention to the fact that he had legs - since it seemed a selling point. Sherlock might be the more experienced manipulator, but John could influence the undine as well.

Sherlock’s breath caught.

John counted that as a personal victory, but continued to speak in a mild tone. “I bet you were patrolling the island for interlopers.”

The merman canted his head to the side slightly in agreement, eyes fixated on the place where John was gently rolling the emerald curtain of his fins between his palms, plucking at the frilled ends.

“Come to me,” Sherlock whispered.

John shimmied up onto the gravel shoal with his weight upon his elbows, and tilted up his chin that he might regard the undine from below. This position seemed to please Sherlock greatly, for he made a little noise in the back of his throat that was more cetacean than human.

John smoothed his palm over the cannon-black scales that interlinked down Sherlock’s tail. He lingered over the single white scale. For all Sherlock’s fantastic anatomy, that tiny mismatched scale charmed John the most.

“This is fetching,” John said. “I noticed it the first day you spirited me away.”

Sherlock’s gills slowly flared out. John was not sure what this body language meant; he had come to recognize gill fluttering as a sign of embarrassment or anxiety, but this was neither. The undine’s breathing was so quick and shallow that John wanted to nuzzle into the heaving demarcation of his abdominal muscles and kiss the skin there until Sherlock gentled for him.

Deliberately, John dropped his gaze lower - to Sherlock’ inguen. The undine’s impressive cockstand had not yet made its debut today, although the vent that housed it was flushed. This was a part of the undine’s body that still had John mystified.

“If I might inquire -?” John leaned in close and let the heat of his breath ghost over that vulnerable place.

Sherlock’s pelvic fins quivered with the effort of not clapping closed over his most private anatomy. John took one in hand as casually as he might the hand of a lover, soothing down its length.

“You might,” Sherlock allowed. His pale eyes glittered.

John telegraphed his intent by moving his hand slowly from the crest of Sherlock’s hip toward the V of his inguen. Sherlock’s pelvic fins twitched reflexively, but did not arrest his progress; John settled his palm over Sherlock’s vent, which radiated heat.

“You are hot. I would bet a groat that you’re hot! How, then, is it that I do not see evidence of this? You can control your..?”

“It would be inconvenient for mine own _cock_ -” here, Sherlock clicked the velar consonant sharply and it sounded so very lewd that John’s cock thickened - “- to emerge every time mine own body experiences arousal. Swimming would be maddening. I assure you, John, I am quite aroused.”

 _Fascinating._ _And so very peculiar._

Sherlock sucked his lower lip between pointed teeth, and then stared at John from beneath a lace of black lashes, long enough to cast a faint shadow on the protrusion of his cheekbones.

John lowered his head in order to skate his cheek along the base of Sherlock’s pelvic fin. He felt the muscle there twitch in response. The scales were so minuscule on Sherlock’s inguen that they felt soft on his cheek, not sharp-edged in the slightest.

John breathed out warmly over the merman’s soft genital vent and Sherlock’s hips bucked. He cupped the back of John’s head, cradling it with his webbed hand, but did not attempt to move him. John’s eyes crinkled mischievously.

“I say old boy, it seems your cockstand has gone amiss. Shall I go looking for it?”

Sherlock wasn't fast enough to hide his snort of amusement, and John ducked his head in order to kiss Sherlock’s vent. The undine made a surprised little sound as John darted out his tongue and tasted clean, salty skin. He parted the skin, just barely.

It was slippery within. Velvet-soft. _Warm_.

It appealed to a very male instinct in him and John groaned aloud. The undine was not possessed of the petals and pearl of a woman, here, but John gave great gamahuche and was thrilled for the opportunity to demonstrate. He dipped his tongue into the molten wet and licked lavishly.

Sherlock took in a gratifyingly strained breath.

John pointed the tip of his tongue and lapped, tiny flicks that had Sherlock’s clawed fingertips twitching against his scalp. He settled more comfortably on the shoal, leaning most of his body weight upon Sherlock’s tail, then brought two fingers to bear and dipped the very tips inside.

“Oh, yes,” purred Sherlock.

John smiled, swirling his tongue. He pushed his fingertips in a little more, then withdrew them. The undine rumbled deeply. John kissed Sherlock’s vent and relished the obscene suckling sound of it, slipping his fingers in to the second knuckle. He rubbed gently up and down that tender, inner wall. Breaching Sherlock was easy and soft. The undine’s body was so naturally receptive that John throbbed with need, and he felt the tickle of warm pre-come trickle down the underside of his cock.

John curled his fingers carefully towards himself, come-hither, and Sherlock went slack with a gasp. The undine’s pelvic fins were shivering. It was an amazing sight, to see Sherlock’s impossibly long, huge body writhing in the surf. Something predatory inside of John licked its chops.

It took Sherlock several attempts to speak, and when he did it was breathy and weak.

“M-Mine own...”

John hummed and lilted upwards at the end, a primitive approximation of a question. His tongue was occupied.

“John, it _aches_ -”

John withdrew, glancing up in some alarm. “It hurts?”

Sherlock’s expression was dazed. He looked as though he could barely think, and when he spoke his voice was soft and slurred.

“I… it aches, John. Oh how it _aches_! I need you..!”

John sat up and cupped Sherlock’s cheek, staring into those W-squiggled pupils with concern. Perhaps that area was too sensitive. Sherlock’s hand came up and covered John’s, pressing it into his own cheek and inhaling deeply.

_I have never seen him act like this before._

“Sherlock? What do you need, pet, come on then. You must tell me; I do not know!”

John could see the reflection of the ocean in Sherlock’s seaglass-colored eyes.

“I need you to _fuck me_ ,” Sherlock whispered.

John’s cock pulsed so hard that for a moment he was afraid he would quite spend his pleasure right then and there. He bit his lip hard that he might ground himself, pull himself back from the precipice. _I hadn’t realized I was that close._ But Sherlock was not done.

“I want you to - to put your cock inside me, right _here -_ ” Sherlock shoved a hand down between their bodies that he might nudge his knuckles into the soft slip of his own body.

“ _Christ_ ,” whispered John.

“Leave them out of this. Put your own hard cock inside m- _yesssssss!_ ”

John’s knees slid in the gravel when he swung a leg over. He nudged the flushed crown of his cock against Sherlock’s vent - recalling the rather hefty penis that was evidently suppressed there. It did not seem to be making an appearance at the moment, however, so John sunk into that delicious wet heat. He utterly failed to take it as slowly as he had initially intended, but Sherlock’s blissful sighs encouraged him.

The undine was a writhing picture of intemperance right there on the shoal of the lagoon. Sherlock's pelvic fins gripped John’s hips, folding around his buttocks possessively and preventing him from withdrawing very far.

“Sherlock, love, I don’t think I shall be long for this -” John utterly lost his train of thought, then, for Sherlock _did something_ then, inside, a sort of rhythmic squeezing that banished all coherent thought.

“Yes, John, perfect. Mine own perfect little human, mine own Riptide lover,” Sherlock crooned, his voice suffused with the supernatural echoes of his Song.

His smile spoke of years of experience, and in that moment John was keenly reminded that Sherlock was older than him - much older - and would likely live much longer as well. Primal in his sexuality, the undine smiled knowingly up at John. Sherlock’s hair spilled in wild black ringlets over his forehead, giving him a rather rakish appeal. But for the subtle gleam of dark scales on his cheeks and brow, the merman looked - well, he looked almost human.

There was a thought.

John could almost imagine Sherlock as a human lover, some fresh young gentleman with too much money and no concept of working for a living. John would pin him with the scarred and knotted weight of his body, hardened from years of physical labor, fuck him until he sobbed with pleasure, fingers gone white-knuckled on John’s unmoving arms.

But almost as soon as he conjured this fantasy, John realized he did not want that. Sherlock was undine. His body was woven from the ozone scent that preceded thunderstorms, and sculpted by the sea. Imagining him as a land-beholden human was just wrong. Then coherency took flight, for Sherlock was pushing his hips up that he might further impale himself.

John groaned and obligingly pushed deeper until there was no space between them and their hipbones ground together. Sherlock grunted in approval, then John withdrew in order to experience that sweet reception once more. He fucked Sherlock, losing himself entirely in the sensation of rutting and penetrating and the embrace of velvet flesh.

And then Sherlock had something to say. Many things, in fact.

“I wonder what you are thinking right now, mine own. D-Do you wish to see me genuflect, a great _monster_ submitting to your will? Does mine own human enjoy the idea that he may own me, that I may receive him inside mine own body - and thank him for it?”

 _Don’t listen, don’t listen, don’t listen_ , John thought to himself, even as those filthy words caused his rhythm to falter. Growling something unintelligible, John snatched Sherlock’s wrists and shoved them down into the gravel above his head. He spared no consideration for gentleness. Sherlock could handle it.

Sherlock gasped and bucked up to meet the slap of John’s hips eagerly. The muscles of his flat belly rippled handsomely with the effort. John risked moving one hand from where he pinned Sherlock’s wrists, that he might press his palm against that whipcord strength and revel in the knowledge that the undine desired this.

He had worked up a good rhythm now, watching Sherlock's features go lax with with rapture.

“Yes, John -! so good, so thick. You stretch me open, I need you to fill me – I'm so empty without you. I need your seed. You'll give it to me, won't you? I want to hold your essence inside me, carry it. If you had a clutch to give me, I would carry it for you. Mine own John, such a _good_ John, yes, _yes_ -!”

John’s breath grew ragged, his rhythm broke into a staccato slap, and then he was coming, his body singing with pleasure, spending into the hot hug of Sherlock’s receptive warmth. All the while Sherlock murmured nonsensical encouragement into his ear, tightening his arms around John possessively. John's blood sang, his breath came harshly from his lips, and although the fog of his paroxysm had not yet faded, John's cock was still hard. He slowed his pace, rocking his hips cautiously while Sherlock nosed at his wrist.

Although it hadn't happened in some time, John was capable of spending twice in quick succession. The second paroxysm was never as strong or productive as the first, but this trick had always been exceedingly well-received by lovers. He decided to show Sherlock, and did not dismount.

"I'm not finished," John growled, dropping his head to pinch a sliver of skin on Sherlock's jawline between his incisors.

Sherlock's brows went up and his mouth parted in a silent little 'oh'. He had been nuzzling at the place where John still held his wrists above his head, clearly contemplating another bite. John tightened his grip warningly, and kept on doing so until he felt the bones in Sherlock's wrist grind a bit. Sherlock practically purred.

He began to speed up.

"John," Sherlock sighed rapturously.

John's muscles were cramping but he ignored it in favor of chasing sensation: he held Sherlock's wrists in a vise grip and pounded into him until each thrust forced a huff from his undine lover. He could feel his own hot spend glossing his affair inside Sherlock, and there - _there_!

It was as though a line of pleasurable electricity was drawn from his bollocks all the way up through his spine, tightening his nipples and thickening his cockstand a second time in the silken sheath of Sherlock’s body. Muscles deep inside his body contracted hard, and John pushed air out from between clenched teeth in a sharp hiss.

This encore was torn from him like an exorcism, leaping over the thin line between pleasure and true discomfort but John wouldn't change it for all the wealth in the Royal treasury. His limbs quivered with exertion and his mouth dropped open at the intensity of it all.

Sherlock undulated beneath him. His voice was drunk with sex and satisfaction.

“Thank you,” gasped Sherlock reverently, lost to the glossolalia of lovemaking: “John, oh, _yes_ , thank you. So warm inside me. I need it.”

The Song’s influence pushed layers of sincerity onto Sherlock's words that forbade any skepticism on John’s part.

He hid his face into the hollow of the undine’s bony clavicle.

John's heart was thudding painfully against his ribs and he was choking on every inhale. Sherlock extracted his wrists from John's grip in order to pet the back of his head. He continued down, following the dip of John’s spine and coming to a rest on the curve of his arse. Sherlock kneaded the muscle, oblivious to the social connotation that the gesture might have carried had he been a human man. He just seemed to appreciate John's arse on its own merits.

John was desperately oversensitive but his back muscles had turned to syrup. He tried to dismount. He failed spectacularly. The undine's pelvic fins held John in place with lazy strength.

"Uuuhnn, Sherlock," John protested. Sherlock’s body was hot inside - almost unbearably so.

Sherlock ignored him, instead opting to Sing quietly. His voice rumbled out in its peculiar multiple layers over the sea. John's body was slippery with sweat, and Sherlock’s breath felt cool against his skin.

“Not yet,” whispered Sherlock, voice silken over the lazy hum of his siren Song. He had an expression of absolute bliss on his face, the smug and sated look of one who had achieved every goal he had ever set for himself.

Some time later Sherlock sighed and relaxed his grip on John’s arse. John lifted his hips more quickly than he had intended. They both gasped when he slipped free. John fell to one side of Sherlock's torso, arm belted across his belly.

A very male curiosity came over him, then, and John looked down the length of his lover’s body. Sherlock's genital vent was plump from sex, the fine scales around it gleaming with slick. Sherlock folded his pelvic fins over that place, veiling evidence of John’s pleasure inside.

John's cock throbbed weakly. Sherlock's tail, huge as it was, coiled eel-like around John's legs and he fell back onto the shallow slope of gravel. The heavy band of the undine's more fantastic anatomy brought to mind an unfathomably enormous serpent. And damn if that wasn't an apt comparison! But what did that make John? A mouse, perhaps.

"Who ever heard of a snake loving a mouse?" John said.

He hadn't been expecting a response. In fact, John hadn't even meant to say such a thing aloud, especially to Sherlock, who had a demonstrated deficiency in comprehending what he perceived to be sentiment. So it rather surprised John when Sherlock replied in similarly whimsical query.

"Who has heard of a bird loving a fish?"

John froze with his nose pressed into the soft demarcation of Sherlock's gills. Did Sherlock know the depth of his regard? Before John had time to conjure a response, Sherlock continued as though nothing out of the ordinary had been said.

"You enjoyed that, mine own," Sherlock told him.

The way he said it sounded very certain. He said it as though he was informing John of something very basic. _The sun rises daily, mine own,_ John thought to himself in Sherlock's voice. He breathed quietly into Sherlock's neck. He did not deny it.

"You may have me again," Sherlock added imperiously, like a benevolent Sultan bequeathing a great gift upon a serf.

John snickered. "You cock. So, that's - that's something you enjoy, then?"

“Yes,” Sherlock breathed, rocking his hips lazily as though chasing the phantom sensation of John’s cock. "It's only natural."

“Natural! Was that - is that something your kind does?”

John couldn’t seem to sift through the pea-soup of his thoughts quickly enough to articulate his concerns. Sherlock hadn't met his small death, and John was a considerate lover. But he was also experienced enough to know that sex did not always mean achieving mutual paroxysm. He decided to follow Sherlock's lead.

Sherlock paused. It seemed to occur to him once again that John was not, in fact, undine and therefore did not know a damn thing about the intimate habits of mermen.

“After the male fertilizes the clutch – yes, _internally_ , John, I can see by your expression that is what you're wondering – the female returns, usually after several subsequent couplings, to deliver the eggs into his brood pouch.”

Sherlock paused here, sensing John's burning desire to blurt.

Sure enough, John blurted. “ _What_ pouch?!”

Sherlock raised his eyebrows.

“Brood pouch. You just spent into it. Quite spectacularly." Sherlock flashed his pointed teeth in a bright grin.

John blinked. He looked, but Sherlock's modesty was preserved by his folded pelvic fins. Sherlock dropped his hand to his hip and crooked a finger in an 'eyes up here' gesture. In doing so, John caught a brief glimpse of the red scar where he had stabbed clean through Sherlock's palm.

The slashed scar on John's own palm throbbed in response.

John took Sherlock's huge hand between his own. He spread the undine's fingers until the webbing between stretched transparent silver, then he leaned in and kissed Sherlock's palm. He tried not to tickle with his whiskers.

"Let me see it, pet," John spoke into the salt-sweet skin.

Sherlock clicked in pleasure and scooted back onto the shoal, until his hips were no longer submerged. His pelvic fins parted like sleek curtains.

John reached out and ghosted the pad of his finger along that freshly-fucked entrance. Sherlock inhaled sharply, but his seaglass eyes were softer than usual when John glanced up to assess his expression. John pressed his finger against the entrance to Sherlock's body, swirling just the tips inside. He had done this, he was directly responsible - he had fucked Sherlock to pliancy and openness.

John dipped inside a bit.

They both moaned.

John pushed a second finger in alongside the first and opened them, spreading Sherlock open. It was pink and appealing within, and John saw that his own seed had slickened that channel. And John was curious. He wanted to know, but the timing was poor. Sherlock sat up somewhat.

“Where does your seed go, or where is mine own turgid flesh?” he offered mercifully.

John was grateful for his lover's perception, as it saved him having to think of an inoffensive way to ask where Sherlock's penis had absconded to.

"The latter.”

“I, like all males, have control over that part of mine own anatomy. I choose now to keep mine own flesh dormant. It surprises me that your own kind’s vulnerable anatomy is unprotected. What if it is bitten off?”

John barked out a laugh.

“Well! That is generally not a risk for landlubbers. It seems to me that your kind really do have the best of both worlds. I must admit it rather boggles the mind.”

“Humans are easily boggled,” Sherlock agreed sympathetically.

John rolled his eyes and thumped Sherlock's ribs. He looked skyward with a sigh.

The sun was bright. The ocean was an endless expanse of turquoise around them, sea birds flying above and making all the racket they pleased. The waves slapped quietly against the bracketing shoals of the lagoon, a noise that had become more familiar to John than the sound of his own breath. The clouds drifted on the ocean breeze high above.

John thought he might be content.

~  ~

John had never had sex so often in his life. For the better part of a week, his life was only eating, sleeping, and fucking.

Sherlock's lust ebbed and flowed as unpredictably as the sea, and it was all John could do to weather the storm of him - the deeply chaotic, pleasurable storm. By the end, he could barely keep up with the undine, who was absolutely insatiable.

Not to put too fine a point on it, but John's arse was sore: Sherlock was covetous of the pleasure to be found in John's body. To his irritation, John became accustomed to slickness coating the back of his thighs where evidence of their coupling spilled. He swam frequently and scrubbed his body clean with sand. It was a futile effort. Sherlock seemed to take offense when John was not painted in his spunk.

For his part, Sherlock oscillated between filthy eloquence and mute satyriasis. He liked rubbing his face against John's calves and feet almost as much as he liked having his cockstand sucked, and the vain creature loved being complimented. Such blatant narcissism would have annoyed John had his lover been human. Seeing the way Sherlock curled his tail and preened when John remarked upon his loveliness was hopelessly endearing.

And John was growing addicted to Sherlock's attention. John's kilt had been flung out to sea by the impatient merman days ago. Fearing for the integrity of Algernon Portnay Kirk's linen trousers, John opted to remain nude - at least until he thought Sherlock wouldn't destroy any clothing he attempted to don.

Sherlock reveled in John’s nudity. When they weren't fucking with the desperation of the only two beings left alive on land or sea, Sherlock was stroking John, touching him - cupping his arse and feet and arms just to memorize their shape.

John was in awe of the fluidity of Sherlock's body, the male undine ability to bestow and receive. Sherlock tended to prefer penetrating John himself, but at least once a day the merman would present himself to John as willing catamite, would invite John to mount him and penetrate his silk-hot vent. From this Sherlock derived a different kind of pleasure.

John, too.

It was the most blindingly erotic activity which John had ever pursued with a lover, male or female, and he wished the Riptide would never end  - what if Sherlock's receptivity was predicated upon his altered biological state during this time?

Despite their physical differences, John was an intuitive and clever lover. He learned to take Sherlock's hefty affair in his mouth, in his hand, and between his feet. Sherlock was equally appreciative of all of these activities - and a quick study himself. He knew how to play John like a violin, and his favorite note seemed to be the sound that John made when the undine lavished attention upon his scars.

John had been at sea for nineteen years. His body was marred with countless scars. He had shallow, corrugated silver stripes on his arms from rope burn. He had palms so thickly callused that sensation there would forever be dulled. He had two knotted knife wounds from a brawl turned sour, and the pièce de résistance was, of course, his bullet scar.

Sherlock was obsessed with it.

The undine had shown what passed for restraint for some time, but as they came to a better understanding of each other he began to gradually push his limits. He liked to lick at the skin there, slow, _maternal_ licking that was far more off-putting than arousing. Nothing John said or did could train him out of this habit. It seemed to be an instinct that was not easily suppressed. John was just glad that the bite was healing up without signs of infection.

In this way the Riptide passed. Sex was wonderful and John as red-blooded as anyone, but there was a limit to even his libido.

On the fourth day, Sherlock went mute. This was the period in which John came to truly understand why Sherlock resented the Riptide, for the poor beast could find no relief. It lasted for a few hours, and in that time Sherlock maintained an impressive, aching erection.

He was beyond insatiable.

He pressed John up against the scratchy grotto wall and fucked the channel of his thighs underwater. His moans were more pained than pleasures. John could feel that Sherlock’s cockstand was burning hot, swollen and tender from near-constant sexual stimulation, and yet the undine could not seem to  shed his urge to rut.

John stared into the line of Sherlock’s breastbone where it heaved inches from his nose. He was exhausted of sex himself, his cock soft between his thighs - mind willing, but body weak. He couldn’t imagine how Sherlock must have felt, compelled by his nature to keep fucking despite the exhaustion of his body. The undine was making low, miserable noises under his breath.

John took pity on him.

“Beauty. Gorgeous thing, I know... I know.You’ve been so wonderful, made me feel so good. I wish - that is, Sherlock, you know I’d be right there if I could..! I do so love the feel of you between my legs - and I know how much you love my legs, yeah?”

John wasn’t entirely sure whether Sherlock could even understand English right now. He squeezed his thighs together a little more tightly, until he could feel the undine’s pulse. Sherlock stiffened up suddenly, then, and met his paroxysm in John’s arms.

The merman shuddered so violently that John had to grab his shoulders that he might steady him; Sherlock was quaking terribly afterward and he had a dazed, sex-fogged expression. His beautiful, moth-delicate hands were palsied upon John's hips.

“There we are. Doesn’t that feel better?” John whispered. _Please let it feel better. I can't stand feeling so useless._

Sherlock keened low and miserable, shoving his face into the crook of John’s arm and hiding there. It was ridiculous, such a large creature taking refuge near one near half his size. Sherlock's tail writhed slowly in the current behind him, piles of vibrant plumage creating a green-blue miasma underwater. His affair was still hot, hard, and huge..

“Let me see,” tutted John.

Something about the undine's state inspired a surplus of compassion. How had he ever thought Sherlock was a monster? John blinked, and realized with an irritable jolt that his companion was Singing under his breath again.

John set a boundary. "Oi! Put a cork in it, pretty boy. I'll be wanting to know when my own thoughts are my own, thank you very much."

Sherlock sighed and rolled onto his back, displaying his affair. The Singing stopped. His eyes were at an exhausted half-mast, looking so tired that if John could have he would have forced sleep upon his lover just to give him some respite.

It was hard not to look at Sherlock's cock. It was just so very prominent when it bothered to make an appearance. Any man would look, John told himself.

It lay in a S-shaped curve, pointing up along Sherlock's belly; it was mightily tumescent and the skin was glossy coral. As John watched, pre-come trickled from the tip of the fluted crown, following the natural contours of Sherlock’s anatomy until it dripped onto his inguen.

 _How the hell that fits inside me is anyone's guess_ , John thought with a sympathetic twinge of his internal musculature. _And why I return for more is frankly more puzzling._

Sherlock regarded him with sorrowful seaglass-colored eyes. He was obviously on the hunt for a good pampering. Luckily for him, John was in an accommodating mood.

“I know, I know,” he murmured, stroking silk-dark curls. “I don’t know what to do, pet. There’s a lad, you’ll make it through this. You've done this before. You can do it again."

But Sherlock's pulse was visible in his neck, and his lips parted to expose just the tips of his bone-white teeth. His eyes became glazed with lust. John watched, a sympathetic bystander, as the undine was slowly sucked under by the relentless pull of the Riptide once more.

~  ~

John was sick of the Riptide.

He hated it.

He was tired of sex, worried about Sherlock, and starving for something more to eat than just fish. He hadn't been out of the damned nest - er, grotto, in almost a week. He was stir crazy, hungry, and ready for some solitude.

The undine was sleeping, draped like a wet black panther over the top of the flat rock. He looked utterly debauched. His black hair was a wild tangle of curls, his fins splayed clumsily out to either side of his body and crumpled beneath his weight with no consideration for artistic composition. The delicate skin beneath Sherlock's eyes looked bruised from sleep deprivation. His fins, presently a fetching seafoam-green, were fading back to white.

John smiled despite his irritation. With any luck the Riptide would see itself out soon and Sherlock would be back to his energetic usual self. In the meantime, John was going back to the island to forage. The risk of encountering a female undine in the open ocean this late in the progress of the Riptide was slim, but John was so determined he would arm-wrestle a mermaid for a chance at food that wasn't raw fish.

The onions called to him.

The _onions._

Mouth watering in anticipation, John waded over to the ziggurat steps. The few items he has appropriated from the islet of bone were laid out here, and it was a good thing those linen trousers fit because Sherlock had taken offense to John's kilt and torn it to ribbons. Although John was now accustomed to nudity as any wild bird or beast, he still enjoyed the air of civility donning trousers lent him. It was a nod to a different time in his life, a time when clothing was necessary. A time when John actually gave a fig about the impression he made. Not that John had seen any other humans for almost three months. He was beginning to lose track of time.

John tucked the knife between the small of his back and the waistband. The hemp rope sheath he had made was fraying to bits already. With one final glance at Sherlock - still dead to the world - John picked his way carefully out into the ocean and began the swim back inland.

He recollected that there had been a time he was less confident of making this particular swim. But John had done it so often now that he hardy ruminated upon the risk. His muscles had grown strong and suited to the task.

In fact, John's mind wasn't even on the supernatural guardian currents that made the trip so perilous to begin with. He was thinking about delicious food. He was of a mind to eat some of the Jerusalem artichokes in the burlap sack. He would make a fire and bake them, and eat coconuts while he waited. Where had the coconuts come from? They weren't native to the island, John decided - coughing when he inhaled salt spray. Probably from a shipwreck. Coconuts were good at finding their way onto nonindigenous locales.

He alighted on the white island sand.

The ocean sucked heavily at him as he slogged up onto the beach, wet white trousers clinging to his legs. He made a beeline for the crate of victuals, but he was overcome with the oddest feeling that he ought to look over his shoulder - like a prickle at the back of his scalp. So John looked, and what he saw out there on the water altered the course of his future irrefutably.

It was a ship.

A large boat, really, a clipper - built for modest cargo and high speed. They were fashionable in America, John recalled through the sudden quagmire of shock.

All thoughts of onions were forgotten. He sprang up like a waterlogged jackrabbit, flinging his arms from side to side. He had to get its attention. Surely someone would notice. John shouted and dashed up and down the beach, not thinking ahead - just reacting, responding instinctively to the startling and unexpected sight.

He prayed he wasn't hallucinating. He squinted into the bright sun, trying to make out the elegant lettering on the side of the ship. What was her name?

Ah. _The Appledore_.

Just when John thought his voice would give, and that he would have to resort to building a signal fire, the clipper turned slowly toward land. She began making the serpentine maneuvers necessary to approach the island. But damn waiting. John had waited enough.

Grinning brighter than the sun, John sprang back into the ocean and began to swim to meet the ship.

The thought of Sherlock did not enter his mind. 

**Notes for the Chapter:**

> Sparkling reminder that piles of [beautiful artwork](http://jinglebellfic.tumblr.com/tagged/gift%20art) and even dolls inspired by the story can be seen on the blog. Sherlockians are so talented! You can check out folks' stellar creativity in the [#riptide lover](http://jinglebellfic.tumblr.com/tagged/riptide-lover) tag on my blog, as well as peruse reader comments, questions, and song recommendations. The playlist [is here](http://8tracks.com/jinglebell-fic/riptide-lover).
> 
> I've snuck in my own illustrations to a couple of past chapters, if any of you are the sort who like to do a second read through. I can't answer questions about the update schedule - that information can be found on you can find on the blog. Thanks for reading.


	15. The Appledore

**Notes for the Chapter:**

> I will be at [221b Con](http://221bcon.com/) in April. Those of you who might be at the convention and are interested in geeking out about merlock things, keep an eye on my blog for more info! This chapter might seem a bit shorter than usual in comparison to the monsters preceding it, but it's necessary for me to break where I do for narrative purposes. <3

The _Appledore_ was a clipper, with a waspish, sharp profile. She was designed to sacrifice cargo capacity for speed. She had a long bowsprit that extended far out over the water like the horn of a narwhal. The hull was black with with a contrasting sheerline strip at the deck level in acid-yellow. From the topgallants flew two flags: a Union Jack, and a coat of arms, though John could not make out the heraldic design of the latter.

The figurehead was a weeping angel, painted wooden hands covering her mournful face. Her long hair turned into a writhing mass of eels that trickled down the prow with such energy that John wouldn’t have been surprised if they moved when he was not looking.

John knew a good ship when he saw one. Though small, the _Appledore_  was a tall-sparred ship and carried the utmost spread of canvas in her sails. She did not have her own dinghy. She didn’t even have a davit to house one, so it was clear that she had been designed for best speed. Someone had paid a great deal of money for the commission of this vessel. But what was a private English clipper doing out in the Mediterranean?

So light was John’s heart at the prospect of freedom that he was not thinking ahead at all as he swam to meet the _Appledore_. He thought only to reach her, to get on board. The ship coasted to a crawl that John might come up alongside her without getting sucked underneath. He lunged forward and snatched the heavy cargo netting that was let down for him; nimble as a monkey, he climbed the side and swung over.

John saw that the hull was in better condition than the deck. There were deep symmetrical scores in the wood – five of them, and each about two or three inches apart. Splinters stuck up from these grooves like errant blades of grass, swerving sternward. The boom showed similar damage.

He glanced around for the crew.

Twelve men would be plenty for this miniature ship - and yet he saw only… five? _Five is a skeleton crew._ John could make out two blokes all the way aft on the bridge: a well-dressed African crewman, and a short ginger fellow with more freckles than skin to hold them. The former was staring down the length of the ship at John. The latter, being the helmsman, was focused on the wheel.

Two more fellows were presently wrestling with a large contraption on the quarterdeck, somewhat closer to where John had alighted on the forecastle. One was brown-skinned with shoulder-length, curly black hair. The other was fair-complexioned with greasy blond locks plaited in a thin rope down his back.

And on the forecastle (where John stood presently, dripping) were the last two members of the crew. A sun-bronzed bloke had hair so startlingly silver that John was surprised to note that the man was of an age with him. He wore dun trousers with leather braces over a linen shirt. He had eyes the color of polished wood.

But it was the last man on the _Appledore_ that most arrested John’s attention.

He had a full head and a half on John, towering over most of the crew like a heron standing over fish. Although the crewmens’ garb was all of good quality, this man was decidedly best dressed. He wore expensive leather boots, white linen trousers tucked in. A navy blue tailcoat framed a brocade waistcoat that would have been more in fashion a decade ago. Round spectacles perched on an aquiline nose.

John had never before seen a yet-living man's face that so resembled a skull.

It was not a difficult deduction to understand that this man was in command. John found himself standing at attention, the knotted muscles of his back tightening. He wished he had put on Algernon Portnay Kirk's shirt before he made the swim back to the island. He was keenly aware of how barbaric he must look.

“Hello,” John said, determined to prove that he was well-mannered. "You would not believe the time I have had!"

It was hard to deduce the man’s expressions, masked as they were by a salt-and-pepper blond goatee.

“It is fortunate I happened to be in these waters, stranger; I see you have been living a difficult life of late,” spoke the spectacled man. John could not place the barest hint of accent that underlaid the man's otherwise precise English. “And who might I have the pleasure of speaking to?”

Oh. Of course. Folks in polite company introduced themselves. Being marooned had done nothing to alleviate John’s natural chariness.

So belatedly he said, "My name is John Watson, of Her Majesty's HMS Endymion. A storm struck. In all my years I’ve never been plucked off-deck. It only takes once, I suppose. Who do I have to thank for my rescue?”

As John spoke, the heron-like man flicked his hand. Though small, this gesture startled the silver-haired crewman; like a well-trained dog, he went back to repairing the deck.

“I am Magnussen. Charles    Augustus    Magnussen.” John had a feeling he was supposed to recognize the name. “I see you have been stranded for some time.”

“Upward of two months, to my ken.”

Magnussen hummed in acknowledgment. The timbre and depth of his voice reminded John of Sherlock – although Magnussen's baritone was less velvet and more gravel.

_Christ. Sherlock._

“Well, Mr Watson. That island must be bountiful in victuals. I imagine you will be wanting to return to civilization as soon as possible, and I regret that I cannot accommodate you with any immediacy.”

John squashed down his worry: he needed all of his faculties to deal with Magnussen.

He replied, “That is all right. I am fortunate to have found a vessel at all; I had resigned myself to living out the rest of my days knowing nothing but the taste of fish and coconuts! I cannot tell you my relief to see men once more. But what brings an English vessel to these waters? And for that matter, where is the nearest port?”

“The nearest port is hardly a port at all, I am afraid - a fishing town with a paltry populace. We will be returning there once this venture is resolved.”

“What venture is that?”

“It is a research expedition. Should I succeed, I will revolutionize the natural sciences -” here Magnussen paused as though searching for an addendum, which he came upon after the barest of pauses. “- for the benefit of mother England, of course.”

“That sounds grand,” John said, and meant it. He gestured to the deep scores in the otherwise pristine wood of the _Appledore_. “I see your vessel has taken some damage.”

Magnussen used his index finger to slowly adjust his spectacles. “She has. Tell me, Mr Watson; what do you see?”

John knelt by the damage, bowing his head to disguise his expression while he stared at the deck. In truth, he knew of only one creature strong enough to shred through solid wood with its claws. And that particular creature was, God willing, still asleep in his sea cave.

_Calm down, old boy. You were just with him naught but an hour ago. These marks must have been caused by some other sea beast, some animal you have not yet seen. Who knows what creature this Magnussen fellow may have encountered._

“I don't rightly know,” said John.

But Magnussen pressed. “Surely you can hypothesize from the available data.”

“It looks like claw marks,” John allowed uncomfortably.

“Precisely,” Magnussen said. “How long have you been on the sea, Mr Watson?”

“Nineteen years.”

“Ah, nineteen! I suppose you have seen all manner of sea creatures in that time, haven't you John? May I call you John?”

The use of his Christian name was unnerving. It removed what small sense of control John had.

He was silent for too long.

Magnussen amended, “No, I am being presumptuous. Watson is how you introduced yourself to me, and Watson is your name.” The _isn't it?_ was implied.

John held his ground. The sound of the sails snapping in the breeze seemed as loud as gunshots. Magnussen clasped his hands behind his back and began to tread a slow circle around John. His boots clicked on the hardwood. _Ch-thnk. Ch-thunk. Ch-thnk._

“Why, look at that great tooth you wear. Where did you acquire it?”

John became acutely aware of the weight of Olizarat's fang on his sternum. _Damn_.

“I found it,” John said, turning his head to keep Magnussen in sight. It took willpower not to turn his whole body that he might prevent the stranger from having the advantage of him. The weight of the ivory knife, still tucked into the waistband of his trousers, was a comforting press against his lumbar dip.

“Curious.”

“I thought so as well,” John replied without missing a beat.

“You see, that interests me twofold: firstly, from the perspective of one who appreciates the natural sciences. That is obvious. Secondly, from an intellectual - no, _psychological_ perspective. Tell me Mr Watson, have you read Bain? No? He is quite the advocate of pragmatic empiricism... I digress. Does a man adorn himself when he is alone on an island, fighting every day for survival?” Magnussen regarded John through flat blue eyes that seemed to defy the reflection of light.

John stared evenly back, although anxiety was an icy finger in his navel.

“I beg your pardon for inflicting upon you my idle thoughts. You must be famished. I’m afraid we are running low on provisions; nevertheless, I believe I have some bread and a vintage of wine.”

Magnussen gestured toward the steps that led down to the belly of the ship. Drawn in by his curiosity like a fish on a line, John descended into the shade after him. But the transition from open air to the confined ship belly made him anxious. He had to stop and breathe slowly through his nose until the sensation passed. John had been wriggling in and out of tight spaces his entire life. This was the first time leaving the open air had ever rattled him. At least the confinement of the grotto had been less obvious than this. He wished that he was back with Sherlock. He imagined cool breath at his neck and strong arms sliding wetly around his waist.

Magnussen left the door at the end of the narrow hall open for him.

~  ~

Magnussen’s personal cabin took up the majority of the ship’s carriage. John suspected that this generous design was at the expense of the crew’s sleeping quarters. He wondered why Magnussen did not lodge in the quarterdeck, which was by far the more desirable location. Officers generally slept above deck.

The whole room was musty with the scent of damp fabric and a faint vinegary odor. There were two wardrobes nailed to the floor, which sandwiched the pristine single bed. The space was monopolized by a mahogany work desk.

Upon this were arrayed a plethora of curious items. A cobalt-blue lamp in the Chinese style sat beside a domed glass display of stuffed songbirds, against which leaned no fewer than four leather-bound tomes. Magnussen lit the lamp, for the porthole alone was not entirely sufficient.

A calligraphy kit with a wooden-handled dip pen lay open on the desk beside an unfinished charcoal drawing of different types of fish tails, meticulously labeled. Most wall space was occupied by glass-paneled display boxes of other specimens. There were butterflies, moths, frogs, spiders, and rodents. There was a bias toward aquatic life, though - fish in particular with their little waxy eyes staring sightlessly.

Magnussen set about preparing a plate of summer sausage and hard cheese, but John hardly paid him mind in favor of trying to guess what was behind the back wall of the cabin.An enormous blue-and-bronze brocade curtain was drawn shut there. The curtain fluttered with the ship’s movement.

John was made uncomfortable by the evidence of Magnussen's wealth, and the general mad clutter. Magnussen’s cabin was a natural scientist’s dream, but John was a sailor. To him, all of the taxidermied specimens just seemed like a waste of food. In addition to that, seeing so much evidence of human complexity after months on the island was... jarring.

 _Well Watson, you are officially out of your depth_.

Magnussen was about as emotive as a corpse, but John got the feeling he was drinking in John’s reaction. His voice jolted John back into the moment. “Please, eat.”

“Thank you,” John replied automatically.

A plate – wood, so at least one thing in this room was practical – of victuals was set before him, and with this a cup of wine. Of the latter John quenched himself with more speed than was polite.

It was good.

Magnussen leaned on the edge of his work desk and watched him. “So Watson. You’re rather less malnourished than one would expect, given your circumstances! Have you family back in England?”

John swallowed around a lump of sausage. It tasted too salty, too flavorful, too much. “I have a sister, although we see each other rarely enough, even excusing my present circumstances.”

“What will you do when you return?” Magnussen wanted to know.

John’s chewing slowed and his brow furrowed. That was a heavy question. 

“Ah. Please excuse my forwardness,” Magnussen said, refilling John’s wine.

“I value a man who speaks plainly,” John replied, injecting his voice with the tone of a man who is grateful to be unmarooned. But the truth was, this was all happening so quickly - and _Harry_ was the family thespian, not John.

He felt like an animal that had been thrust into a situation it did not understand. He wanted to step back in time, to retreat and observe from a distance. Damn his rashness! And yet, if he could wind back the clock... John was not sure what he might have done differently.

Although John had left Sherlock contented, he could not forget that the undine had captured him. Their relationship had been unequal, bizarre, and frankly degenerate from the beginning. And now John had done it. He had found a means to escape the island. He would have been a damned fool not to take the opportunity. He should be rejoicing, no, he should be _weeping_ with gratitude. He should be dancing a jig!

Magnussen would drop him at the fishing village on the large island, and from there John would plan a course back to London.

This was what he had wanted all along.

So why couldn’t he stop wondering what Sherlock was doing at that very moment? What would happen when Sherlock realized that John was gone? The undine would be livid. He would most certainly go looking for John. John hoped that he would be safe from recapture aboard the ship. Without legs, climbing aboard would be quite a Herculean task. Besides, he remembered Sherlock telling him that undine didn’t make it to adulthood without a healthy aversion to being seen. It was why they waited to ambush drowning people instead. John remembered the little smirk on Sherlock’s face as he had drunk in John’s reaction to _that_.

No, Sherlock would probably deduce that John had left with the ship. He might throw a monstrous strop, like a child having lost his treasured toy, but in time return to storm-chasing and collecting other sunken treasures. In Sherlock's long lifespan, John supposed he was but a single fleeting moment. His heart grew heavy.

The whisper of fabric on steel summoned his focus from his own thoughts to Magnussen, who regarded him through unreadable eyes. He was cleaning the knife he had used to slice the sausage with a handkerchief.

Christ.

An _embroidered_ handkerchief.

The luxury of it disgusted John, the excess of money and material wealth suddenly not merely ugly but offensive to him. Men like Magnussen, possessed of old money and too much ambition, annoyed him profoundly.

“Mr Watson, your expression could subdue a shark.”

 _If only_.

“Beg pardon,” John said, using the napkin provided to wipe his beard, “but it seems to me that this vessel is shorthanded. Would the damage on deck have anything to do with that?”

Magnussen's smile faded.

“It is so. I began my expedition with twelve, but just two days hence we met with a great breakthrough – unfortunately, at the cost of seven of my crew.”

“Seven!?” said John, inwardly aghast. What man in his right mind would keep at sea after such a disaster? “What could possibly be so pressing as to preclude going back to port?”

“Mm. Look around you, Mr Watson.”

John blinked. He searched Magnussen’s face with narrowed eyes. He did not know what direction the naturalist might next pursue, and stayed silent lest he condemn himself. Thankfully, Magnussen began to speak anyway.

“I took interest in the natural sciences when I was but a lad. All creatures fascinated me, and the internal mechanisms by which they operate. How does respiratory function work? How does a lizard change its color to match its surroundings? How do the wings of a songbird compare to that of a raptor? How vast the Kingdom Animalia is, and how minuscule our understanding of it!”

As Magnussen bloviated, a suspicion began to form in John's mind – a thought he had squashed immediately upon climbing aboard, for he so disliked its ramifications.

“Think of how very many species yet lie undiscovered. Flying creatures, digging creatures that creep in the cover of night, swimming beasts cloaked by the ocean. And oh! The ocean is _so_ vast and deep."

All this talk of undiscovered species solidified John's niggling suspicions. The undine were certainly unknown to the world at large. Magnussen was obsessed with documenting new species, and worse yet seemed to be searching for something.

 _He might seek some other creature_ , John tried to comfort himself. _I can't know for certain that my own secret knowledge isn't coloring my perception. Why, I hadn't known about Olizarat or the Listener, either! Perhaps he pursues a sea monster, or one of the Named Ones. He is the one who ought to be afraid, then; any of them could swallow this ship in one gulp._

All John could do now was bide his time. Magnussen would show his hand eventually; men always did. In the meantime, he resolved that he would protect Sherlock however he could. The undine had protected John from the dangers of the sea: it was only decent to protect Sherlock from the dangers of men.

"I intend to illuminate the mysteries of the deep, and this region is positively enshrouded in mystery, Mr Watson. _Enshrouded_. Once again, I simply must refer to that peculiar tooth you wear as an example of this! I wonder if I might see it."

It took effort to feign nonchalance.

Sherlock had given John Olizarat’s tooth, and it had replaced his old bullet pouch as a lucky talisman. Sherlock had his bullet now, although John was not sure where the undine was keeping it. He had never seen it around Sherlock's neck. John shrugged out of the crude necklace and passed it to Magnussen, whose hand was cool and dry like a lizard.

“I have not seen a tooth like this before. Where did you say you found it?” Magnussen tested the point of Olizarat’s fang against his palm, pressing until the skin dimpled and blanched.

“It - it washed up on shore. To occupy my time on - on the island, I wove rope and… I thought I might make something,” John finished, cursing his unsteady delivery while his thoughts raced helter-skelter.

Magnussen hummed softly. It was a one-note sound. Conspicuously absent of supernatural overtones. Human. He held Olizarat’s tooth up to the light, turning to examine it from every angle.

John felt naked without something around his neck. His bare toes curled into the hardwood, and his knuckles blanched slowly where he gripped the wooden cup. It seemed like a small eternity passed before Magnussen returned the fang, and when John reached out to take it, he found his wrist taken in a firm grip. Magnussen turned John’s hand to expose the scar on his palm - from where John had cut himself with the razor shell in order to break Sherlock’s siren spell.

John rose so abruptly that the chair clattered to the floor behind him. He jerked out of Magnussen’s grasp and wielded the giant tooth like a knife. His pulse was regular, and his hand was as steady as bedrock. He would have to be fast. If he was quick, he could stick Magnussen in the throat where the skin was thin and marbled with blue veins before he could cry out -

“Apologies, Mr Watson! I thought the wound was new, and was merely checking to see whether you would have need of medical attention.”

There was a glimmer in Magnussen’s eyes that had not heretofore been present. John had not known the man long enough to say, but he would almost peg it as… excitement?

He kept the fang level. He did not wish to be touched.

“Come now,” purred Magnussen, raising both hands placatingly. “I didn’t mean any harm. You must forgive me. It is a rare thing to come across a marooned sailor - especially one in such robust condition. It’s quite the stuff of story books. When you return to London, you will be the talk of the town.”

John was caught off guard. He felt unbalanced, unsure. One minute Magnussen was imposing upon his personal space, and the next he was reminding John that he was rescued. It did not even occur to John to feel oddly about his own homicidal impulse, although such a reaction would never have occurred two months ago. Magnussen had made him feel threatened, so John made the split second decision to defend himself.

Since Magnussen was not responding to the threat of his posture, John eventually lowered the tooth.

“I… don’t like to be touched,” he managed at last.

“Understood. You have been without company for so long after all. Although not perhaps _entirely_ alone -” (John held his breath.) “- for this region is rich with truly spectacular fauna! Cetaceans, birds, sea turtles and countless fish...” Magnussen trailed off, using the tips of his fingers to smooth his goatee.

“I… I am afraid it is naught but sea birds," John said faintly. _  
_

“Mm. Pity.”

Magnussen strolled the length of his cabin. John watched him go. He not bear this skulduggery any longer. _If there is to be a confrontation, let it happen now._

“Magnussen,” John said quietly. “What, precisely, befell your crew?”

Magnussen paused mid-step, placing his foot down carefully before pivoting around to make eye contact with John. “A pertinent query, Mr Watson, and one that warrants a direct answer. An animal attacked us.”

“An animal,” repeated John.

“Yes. A monster, if one entertains such medieval notions. I intended to collect it as a specimen, but... all did not go according to plan. It is a curious species, Mr Watson. I confess to being quite enraptured. I first caught a glimpse of it out on an ocean rock, whilst traveling with my parents as a boy.”

John knew that he was supposed to ask Magnussen what it was that he had seen.

John did not ask.

It hardly seemed to matter, for Magnussen flourished voluntarily at the introduction of his favorite topic. He gesticulated as he spoke, slow and deliberate as a conductor of some invisible symphony.

“Even at that tender age, I knew I was bearing witness to something spectacular. But when I told my parents what I had seen, they were inclined to dismiss it as childish fantasy. It is no matter. I have my evidence at last.” He walked slowly backwards towards the brocade curtain.

“You do?” whispered John.

Magnussen smiled with closed lips. “Yes. I perceive that you are not a man of weak constitution? No, surely not. The island would have claimed you otherwise. Come closer, Mr Watson. It must be seen to be believed. My own crew doubted the veracity of my claim until we came upon the creature just two days ago.”

John was disquieted. This entire scenario was crooked. The cabin seemed too small to contain his dread, which pressed in from all four walls like the smothering weight of a wet wool blanket. On the one hand, he did not want to see what was behind that curtain at all.

On the other, John wanted desperately to know the truth.

A curiosity simmered low and sick in his belly. If he left now, he would never see what was behind the curtain. And if there was some poor creature trapped in the Appledore’s hold that yet lived, perhaps John could free it. So he fortified himself by hanging Olizarat’s tooth once more against his neck, and padded over until he stood adjacent to Magnussen, who was untying the far edge of the curtain in preparation.

He knew that his body language projected his distrust, but he could not be arsed to mask it.

“Behold,” smirked Magnussen, and he drew back the heavy curtain with a rattle.

John held his breath and leaned forward, fingers prickling with anticipation.

**Notes for the Chapter:**

> Yeah, yeah. I know. Two cliffhangers in a row - but this is where I planned to have this chapter break, so we're doing at least _something_ by the book here, damnit. :D And this is the chapter where I get to ask if anybody here likes steampunk? No? Yes? Well, either way hold onto your butts!
> 
> Sparkling reminder that piles of [beautiful artwork](http://jinglebellfic.tumblr.com/tagged/gift%20art) and even dolls inspired by the story can be seen on the blog. Sherlockians are so talented! You can check out folks' stellar creativity in the [#riptide lover](http://jinglebellfic.tumblr.com/tagged/riptide-lover) tag on my blog, as well as peruse reader comments, questions, and song recommendations. The playlist [is here](http://8tracks.com/jinglebell-fic/riptide-lover).
> 
> As always, please check the blog for update information as I can't answer questions pertaining to that in the comments.


	16. Specimen

**Summary for the Chapter:**

> In which John punches a shark into vegetarianism.

**Notes for the Chapter:**

> Dear reader! ~grabs your hand~ I need you to trust me that the story does, eventually, end happily! Because this chapter is gory, violent, and gruesome - and the next one just as much if not more. So just be a responsible reader and double check those tiggity-tags, s’what I’m saying. There are [plenty of other stories to enjoy](http://jinglebellfic.tumblr.com/ficrecs) if this one isn't to your taste!
> 
> My deepest affection to Anarfea, to whom this story is dedicated, and to those beautiful sea stars that lend me their brains and proofreading skills: redscudery, JP, catie-brie, and the Antidiogenes club.

Magnussen drew aside the curtain in his cabin to reveal an enormous wooden box - much resembling a coffin. The coffin - _call a spade a spade, Watson_ \- was utterly practical and unembellished. It seemed to have been constructed inside the room, for there was no way that a container so large would have fit through the narrow door. ****

John looked on mutely as Magnussen unlatched the lid. A vinegary-salt scent flooded the room and John clapped a hand over his nose.

“Yes, the odor _is_ unfortunate. I’m afraid this specimen is excessively fragile. Undiluted seawater seems to be the only mixture that stalls decomposition.”

 _So much for rescuing the poor creature_ , John thought. _It must be quite dead already._

Magnussen turned a crank on the side of the coffin; the top squelched free. A cascade of pink-tinged water flowed down the waxed inner lid and John peered inside. His stomach roiled and it took every ounce of stoicism he possessed not to heave up sausage and cheese.

An undine.

Despite being in poor condition, there was no mistaking the humanlike torso and arms, and the endless ouroboros of tail. It was crammed into the box, fins crumpled underneath its own body.

No. Not _it._

_He._

He was a male undine, distressingly similar to Sherlock in phenotype. And oh! Words could not describe how relieved John felt that the scales he saw were not midnight-black, but abalone-pink and somewhat opalescent. The corpse’s fins blushed red at the hem, swaying slightly with the rocking of the ship. This poor fellow had been in the throes of the Riptide when he died. John’s heart burned – where was this undine’s lover?

The corpse was shot through with incisions and stitches, particularly around the gills. The fins were fizzing slightly and dissolving away before John's very eyes. A layer of seafoam formed where the body rotted. Magnussen used a large wooden ladle to scoop away some of this obfuscating foam, which he poured into a basin to the side.

"This species decays at an alarming rate. I doubt it will last the week, and I only acquired it two days ago," Magnussen hurried to tidy the specimen, seeming put off that John was witnessing its decay. "Would that I had my full laboratory with me! Then I could perform the tests I wish to. It had been my hope to bring this specimen back to London with me, but that is impossible. The decomposition rate is fascinating, Mr Watson, I must say. I find it a relief --”

There was a ringing in John’s ears.

It was a faint high-pitched sound, a pennywhistle off tune, and he found it difficult to focus. He saw Magnussen’s mouth open and close like a puppet, but the sounds coming out held no meaning.

The _Appledore_ hadn't just been coincidentally in these waters. It had been trawling for merfolk.

Which meant that Sherlock was in grave danger.

“-- After so many summers spent in search of evidence of these beasts - a fin, a bone, a scale, _anything!_ \- I rather find it comforting to know that my failure to locate fossil proof was not a marker of ineptitude but, in fact, a clue.”

Magnussen paused to take in John’s stupefied reaction. “Mr Watson?”

John had no idea what emotion he should project. What would be least likely to betray his knowledge? He was at a loss.

“I. It’s… quite something,” he managed.

“I should think so! I would like to hear a layman's impression. What do you make of it, my dear fellow?” Magnussen stepped aside with a flourish, inviting John to peruse the specimen.

John did not step closer.

“I'd say it looks like a merman,” John said, hoping that his quietness would be perceived as shock.

“Mer _man_ you say.”

Too late John realized his mistake. A bead of sweat slid down the nape of his neck.

“Curious that you should guess correctly its sex. The males of this species are quite... floral,” said Magnussen.

"Lucky guess," John said. He tried to steer the subject away from his slip. "What, ah, what is it truly?"

“It is a gift to the scientific community - an undiscovered species. As I am the one who found it, I shall be the one to name it. I think I shall call it 'Magnussen's greater siren', or _homo aquaticus_. In all likelihood these are the creatures from which the myth of the mermaid was spun!" Magnussen smiled - or at least, he twisted his lips into the closest approximation of joviality such a skull-like visage was capable of.

Evidently that was supposed to be a joke.

John was looking at the undine again. The poor thing floated in his own brine. Magnussen reached into the solution in order to lift up the corpse’s stiff hand. He spread the fingers with some difficulty and displayed the webbing between them.

Nausea crept up on John again like the swell of the tides. It was all too easy to imagine the undine as he would have been in life: vibrant and ever-moving. Like Sherlock. This body was an empty vessel, soul and charisma long fled.

" _Mermaid_ has far too fanciful connotations. Look at the talons on this monster, Mr Watson; behold the power in the tail. This species may look superficially human - I suspect we may share a common ancestor, if Darwin's recent publication holds merit - but it was not, in all likelihood, as intelligent as you or I."

 _Wrong_ , John thought instantly, and so fervently that for a moment he feared the word had spilled past his lips. He thought of the diamond-sharp glitter in Sherlock’s eyes, and the undine’s quick retention. _You could not be more incorrect._

“I admit my species bears a certain resemblance to humans, like the merfolk of lore. But it does no good to think of animals as human, no matter how similar we may look. Why, think of the great apes! The principle is the same.”

John grit his teeth together so hard that he felt the moment one of his back molars chipped. The sudden sting of it grounded him. He watched as Magnussen used a pole to prop open the coffin lid whilst humming what John vaguely perceived to be a popular symphony. Beethoven? John wasn’t sure.

“When I was a boy my father brought me a pet. A grey parrot, from Africa. She was a clever bird, so dreadfully clever. One day, she repeated something that she had heard me say. It was astounding! Of course, at that age I thought she really could understand me... as though a minuscule human was trapped inside of her. But then with time I realized that she was merely imitating me, and did not understand anything she was saying. I learned so much from that animal."

Magnussen left the lid propped open and went to his work desk in order to pull out from beneath it a glass-paneled box. This he set upon the cluttered surface.

“By what mechanism could that bird produce such humanlike sounds? I dissected her and inspected her vocal chords and brain. I have done much the same with this _greater siren --”_ _Undine_! John thought furiously, “-- working tirelessly these past two days and nights. Time is of the essence. Soon the specimen will turn to seafoam, which is of no use to me.”

Grey-tinged strips of tissue were spread open within the display box. Like points on a constellation, copper wire connected a series of metal pins to a box with levers and switches set upon its face, which were in turn connected to a strange device that John had missed in favor of lingering on other curiosities in Magnussen’s cabin.

 

A plaster-of-paris barrel was propped at an angle on short brass stilts. The upper end of the barrel was open and the bottom was plugged with a flat metal ring. A membrane was stretched over the center of this ring, and from this protruded a brass tube. A pig-bristle stylus poked out of this hub, its tip poised over a lamp-blacked roll of paper.

John was rapidly losing patience with the whole situation, but he had to keep his temper in check. He had no idea how someone with no familiarity with the undine might react to all of this scientific balderdash. _I must focus. If I do not divine the purpose of this contraption, I will be of no use to Sherlock, and he might meet the same fate as that poor creature. I must protect him._

"What is this?" he asked, aware of the artificiality of his own tone.

Magnussen’s lip quirked indulgently. “These are the vocal cords, in this box - and this is the phonautograph which I have connected them to.”

"This is all quite remarkable to me."

“It is, isn’t it! Remarkable, Mr Watson, yes. Quite remarkable.”

Magnussen unlatched the display box and swung open the glass frame so John could better see the vocal cords, ornamented as they were with meticulous wiring.

“ _M.’s greater siren_ is quite reliant on vocalizations, sonic - sonic _abilities_ , if you will. Like a bat uses squeaking sounds to navigate in the darkness. The _siren_ ’s vocal ability is key to hunting, and their favorite prey --”

 _Humans_ , John thought, an instant before Magnussen said ominously: “-- human beings.”

John tried to look appropriately startled.

“That’s horrifying.”

“Isn’t it? They are monsters, and no mistake. This one tore the throat from one of my men with its teeth. We shall have to stay on guard on our return to London for the vivisection.”

“Vivisection!” cried John.

“Oh yes, Mr Watson,” Magnussen purred. “If this were any other animal I would bring a deceased specimen for perusal, but that is impossible. How am I to study a creature that dissolves into seafoam within days of its expiration? The only logical solution is to bring it to the greater scientific community, and demonstrate its unique anatomical charms. Alive.”

“What makes you believe that it won’t destroy the remainder of your crew? Or you!?” John exclaimed. “This is lunacy. If this creature is as deadly as you say, it would be madness to hunt it. And with a skeleton crew, besides!”

"While these creatures are powerful, mightier beasts are felled every day by whaling ships. Tooth and claw and sinew are easily enough avoided. It was the _greater siren’_ s song that brought my men within its reach. Wax plugs may have sufficed for Odysseus’s men, but with this device…”

Magnussen rapped his knuckles against the wooden frame. “I will frustrate the creature, and in its confusion, my remaining men will subdue it. At the right frequencies, my machine induces convulsions in the _greater siren_. Fear not. I have the proper precautions in place.”

John curled his feet into the hardwood until the bones of his toes ached. He needed to understand Magnussen’s plan in more depth before he could hope to undermine it. _Tell me what you're planning, you scoundrel. Is your crew privy to this madness? Surely sound-minded men would not follow one who claims that mermaids exist._

“It all sounds very vague to me. Are you sure you know what you’re doing?”

Magnussen’s shoulders tensed.

“Vague? There is nothing _vague_ about it. I’ve connected a delicate rheostat of the most modern construction to a larger replica of this very phonautograph, which is presently located above in the quarterdeck. It replaces the writing instrument, the stylus you see here. Sounds picked up by the barrel of the phonautograph change the current that runs into the larynx musculature --” Here Magnussen pointed to some wibbly bit of flesh in the display as though this could possibly mean something to John, “-- changing the pitch of the sound."

The premise seemed astounding, if John was honest, but he was too wary of what this might mean for the undine - for _his_ undine in particular, to praise Magnussen's invention.

"My men are abovedeck preparing the bellows. When operated, air flows through my device and and over the vocal chords within, much as it would have when the creature drew breath.”

"Hold on a moment! Are you saying that you are able to replicate this creature's song?" That was a terrifying premise indeed.

“No, no. That is beyond my capability at this time. You see, every note of music that travels through the ether has an equal and opposing melody. A matched vibration that exactly annuls the motion of the air! Such precision is beyond this particular expedition, of course, but the snare I envision does not require it. I need only safeguard my crew."

John's thoughts took a turn for the furious. This machine, if it functioned the way Magnussen hoped, had the potential to strip away one of the undine’s most powerful natural weapons. Without his voice, what could Sherlock do to defend himself?  _Especially since… since I made him promise not to kill humans. Oh buggering hell, John Watson, you thrice-damned fool! I can only pray he does not venture to this vessel._

John forced himself to focus. “If the flesh rots so swiftly, won’t the… won’t the vocal cords rot as well?”

“They will, and they _are_. As I have said, time is of the essence.”

“That’s why you haven’t gone back to port to regroup and resupply.”

“Quite.”

Magnussen was now occupied flicking levers on the box. He spun a small winch. Tiny arcs of purple electricity danced between the pins in the voicebox, and John could not suppress a gasp. The flesh now pulsed subtly, like a beating heart.

Magnussen practically purred, pleased by John's reaction. “You, my dear sir, bear witness to history in the making.”

“It, ah. It is extraordinary. You've gone to such trouble. Have you come across any others in these waters?”

“This is the first specimen I have captured intact. Even now we are circling the island on which you were stranded – I believe a _greater siren_ lives there.”

John raised both eyebrows. “I can assure you, there is nothing of interest on the island.”

“Can you?” Magnussen replied.

“Yes. I was stranded there for some time,” John told him. He was proud of how solidly his voice emerged, how reasonable he sounded. “If a man-eating siren lived nearby, would it not have hunted me long ago? Perhaps you should try different waters.”

_Or just… give up and go back to London. Perhaps get eaten by a Named One on the way._

Magnussen remained impassive. “That is most peculiar. My current theory is that this species targets lone humans, most likely victims of accidents like the one you suffered. But the timing of this year’s expedition is auspicious. My devices have picked up sounds in these waters --”

"Whales!" blurted John.

Magnussen blinked.

Damnit. _Subtlety thy middle name, Watson._

“Perhaps it is whales," John tried. “I have heard their songs myself late at night.”

“...It is _not_ whales.”

“You sound so certain.”

“And you are skeptical despite the evidence that lies right beneath your nose. One prays the scientific community of London will be more receptive to my discovery than a lost sailor.”

Magnussen tilted his head and slid the tips of his fingers along the frame of the voicebox display. He leaned in close, so close that John could feel body heat against his naked skin and smell Magnussen’s cologne.

John tensed.

But Magnussen reached behind John for a silk rope dangling freely from a square cut in the cabin ceiling. He pulled this and a bell rang above deck.

“I think I shall have a _very_ thorough look,” whispered Magnussen, his breath moist on John's shoulder. John’s stomach plummeted when he realized that this was the very shoulder that Sherlock had bittenduring the Riptide. The undine’s toothprints were still an angry red dotted line along his trapezius.

For a moment, John thought that - _well, no that would be absurd, Watson_. It was just that, for the barest hint of a second, John had been sure that Magnussen was going to _lick_ him.

Not a moment later, the cabin door swung open. Three men crowded in the doorway: the blond-haired crewman, the tall African fellow, and the man with the silver hair. Magnussen stepped back and smoothed his goatee.

“Gentlemen! Please escort Mr Watson above deck. It is time to make good on our mission. I shall join you presently. Omadi, if you would?” Magnussen gestured for the African bloke to stay behind.

Buzzing with anxiety, John made his way back through the belly of the ship escorted by the two crewman. He felt more out of place for his lack of shoes more than for his shirtlessness.

When they were out of earshot, the silver-haired crewman leaned in close. “I’d kill to hear _your_ story over a pint! What’s your name, mate?”

“ _Lestrade_!” hissed the blond crewman.

“Oi, you leave off. Ne’er any harm in making acquaintances.”

“It’s your funeral,” grouched other crewman.

John eyed the other man contemplatively. Lestrade had coffee-colored eyes and a natural lantern jaw. He had a sailor’s build, and the quality of his movement was familiar and reassuring.

“Watson,” John introduced himself. “Sorry to hear of what befell the crew.”

“Me too,” Lestrade agreed. “Did he show you the mermaid?”

The blond crewman interjected again. “Blimey, Lestrade, do you have a _death wish_?”

“Shut it, Almonte. Magnussen ain’t up here right now.”

There was no time to say more, for they came onto the deck and John immediately leaned over the hawser to check their position. The _Appledore_ had coasted up around the island perimeter. They were close to Sherlock’s lagoon.

John’s heart leaped into his throat. There was no way that Sherlock would remain ignorant of the ship. If only he could get the _Appledore_ away from the island and the grotto his lover called home! John would not let Magnussen cull Sherlock like some common beast, or take him away to be picked apart as a curiosity for the voyeuristic eyes of Londoners.

An ill wind had blown him off the HMS _Endymion_ that stormy evening months ago, and John’s luck had only atrophied. But John was stalwart. He had forced Sherlock to breathe for him, refused to give into the siren Song, and through sheer stubborn will had managed to survive in Sherlock’s territory for months. He had come through it - but not unchanged. Something unexpected had happened.

John had fallen in love.

He had never been in love before.

For a moment, John considered what his life might have been had he done the expected thing and married a woman. There had plenty of opportunities to settle down - all the nice girls liked a sailor. Why, if his shore leaves hadn’t been spent taking care of his sister, perhaps John might have encountered a kind-eyed woman who would miss him while he was away at sea. But no.

No, John Watson had to go and fall in love with a man-eating merman.

It seemed blasphemous. If there were a hell, John was surely going straight to it - but John had already made up his mind. He loved Sherlock, he of no surname. That wild ocean creature that whispered dark words against his skin at night, as brilliant as sudden lightning over a quiet sea. His energy complemented John's own like no one else’s ever had.

It was only that their roles were so imbalanced. Had he not felt so useless, John might not have fled. He had certainly not been unaffected by the intimacy he and Sherlock had shared during the Riptide. He sought escape out of reflex and a thwarted desire to achieve balance. John needed to feel as though he could provide something for Sherlock, but by the merman’s standard John was weak. He was tired of being coddled. Now, John could prove himself useful. He would start by keeping Sherlock safe from Magnussen and his ghoulish contraptions.

 _You can’t have him,_ John thought. _He’s mine._

He flinched when Lestrade came up quietly beside him.

“S’a bit much to take in, isn't it?” Lestrade said, misunderstanding the cause of John's introspection. “Magnussen's an odd one, but he isn't wrong about these waters. There are monsters.”

Lestrade followed John’s narrowed gaze. They watched the black-haired man pull a tarp off of what appeared to be oversized blacksmith's bellows nailed to the taffrail. To these bellows were attached leather tubes, stored in careful coils. A metal net was hitched to a second boom.

In all his years, John had never seen anything like it. “What the devil is that?”

“Magnussen’s machine. He's the only one who knows how it works, since the shipwright got - got _eaten_. He keeps the second portion of it locked away in his cabin. It takes some time to put together; the monster was on us before it was ready,” Lestrade whispered, ignoring Almonte's disapproving glare. “It killed Anderson first."

A softer man might have offered an apology, but John had never been inclined towards useless platitudes.

Magnussen and his tallest crewman - _Omadi_ , John recalled - emerged onto deck. Omadi held the undine voicebox; Magnussen had a rifle-musket strapped across his back, and a Lindsay single-barrel pistolat his hip. John’s scar throbbed.

“Mr Watson! I must thank you for being such an attentive audience,” said Magnussen in his deep, soft voice - a voice that carried across the deck without shouting. “But I’m afraid your presence is too serendipitous to pass up. As you know, the _greater siren_ is a man-eater. The only way to lure it from the deep is with human blood.”

_Oh. Time to go._

John pivoted on his heel and dashed to port **,** fully intending to take a nosedive into the ocean. He’d take his chances in the deep, thank you very much! But the blond crewman - Almonte - seized John's arm as he dashed past. John snatched the knife from behind his back and slashed. Almonte gasped and stumbled back, a line blooming bloody across the bridge of his nose. Lestrade was slower to act. John did not care whether this hesitation was motivated by sympathy for him, or incredulity at the disquieting implication of Magnussen’s words; when Lestrade’s arm stretched out for him, John cut it.

Lestrade yelped. He cradled his bleeding forearm, gaze flicking belatedly to the gash on Almonte’s face. “Where was he hiding a blade?!”

“Careful, boys,” Omadi rumbled. He set down the voicebox display and approached with the practiced prowl of a man who knew the value of caution.

John twirled the knife, running his tongue along the cracked edge of his lower lip as he backed up against the bulwark. He was not going to be offered up as some bloodied sacrifice to any undine. After all he had been through! That was not _,_ absolutely not, how John Watson's tale would end. No. He was going to escape. He was going to get back to Sherlock.

Once he was with Sherlock, everything would be all right. They would figure it out together. Now that John had admitted to himself the depth of his regard, the thought of Sherlock brought a little thrill of warm anticipation. The thrill snuffed out when Magnussen trained his rifle upon him. John forgot how to breathe. His scar throbbed and reminded him how cold a small lump of metal could be. John stared into the round black mouth of the muzzle and envisioned a short pop and smoke, a blinding white pressure between his eyes in the instant before death.

He looked up the line of silver leading to Magnussen’s stony face.

“Now, now, now,” tutted Magnussen. He sounded so reasonable. As if John were the one at fault for disobliging. It was fortunate no low-flying gull made a pass over the _Appledore_ in that moment, for the palpable tension on deck would have surely mummified it.

John’s chest heaved and sweat trickled down the corrugated plane of his sun-bronzed belly. He couldn’t take a chance on Magnussen being a poor shot. If he died, he would never see Sherlock again. So he cursed and let the knife clatter to the deck. The crew, with the exception of the freckled helmsman on the bridge, formed a half-circle around him.

“It’s nothing personal, John. Better you than what remains of my crew, trained as they are for this expedition.”

John growled. “This is a fool's errand.”

To his surprise, Lestrade spoke up. “Sir, is this really necessary? Surely we can lure your creature out of the deep using some other metho --”

“Excuse me?”

Magnussen’s voice was soft, but it sliced through the air like a whip.

Lestrade went quiet.

“You’d do well to remember that your daughter’s fate rests in my hands now, Gregory. It makes no difference to me whether it is a Mr Watson or a Mr Lestrade that sacrifices himself to our cause today. Would you rather take his place?”

Lestrade averted his gaze.

John pressed. “Listen to reason! That creature took out half of your crew. Even if a second one should appear, the same fate would befall what is left of you,” John’s gaze skipped from face to face. “Surely his blackmail is not worth your lives!”

“A thespian of quality you are not, Mr Watson. I tire of your performance. Gentlemen.”

They fell upon him.

John did not go down without a fight. More than once he felt the crunch of cartilage beneath his knuckles. But he was overwhelmed, and the crewmen bound his hands and feet with an expediency that showed this was not the first time such a task had been set them. He didn't waste breath calling for help. The only ally he had was Sherlock, and the last thing he wanted was for him to investigate the _Appledore_. John jerked fruitlessly against the tide of arms that held him down and bound his arms behind his back. A rope was tied fast about his ankles.

 _Oh. No. Surely he's not – he couldn’t possibly..._ But it looked like any sailor's worst fears were coming to pass, for the rope was tethered to the starboard bulwark and looped beneath the ship. Keelhauling. The practice had been abolished for its barbarism over a decade ago. Somehow, it didn’t surprise him that Magnussen would do it. John would be dragged below and scraped against the thick crust of razor-edged barnacles on the belly of the vessel. If he didn’t drown quickly, he would emerge skinless and bleeding by the time they hauled him up the other side.

Almonte and Lestrade manhandled him to his feet, shoving him against the bulwark. John could feel the ocean at his back. He glowered, but Magnussen didn't even have the decency to watch the proceedings. Instead he chose to attend to his mad machine. This dismissal filled John with white-hot rage.

“MAGNUSSEN!” he roared.

But Magnussen was calibrating his machine, head bent low over the contraption. “Fletcher, my dear fellow, it is of the utmost importance that you do not stop working these bellows. No matter what may transpire in the oceans below, or even here on this deck – do not stop pumping _._ ”

Fletcher nodded grimly, flexing his fingers in their heavy leather gloves. _Blast._ John put his back into it, struggling to free himself.

“Christ!” hissed Lestrade, adjusting his white-knuckled grip on the heavy rope which bound John's arms. Blood trickled down his forearm from where John had cut him.

Omadi frowned and tightened the rope banding John’s arms to his sides. “Stop.”

John glared down at the top of Omadi’s sleek bald head. “Murderer.”

Omadi faltered and John’s curiosity was piqued. He lowered his voice and whispered, urgently, “He threatened you. Somehow. What does he have on you?”

Omadi had no chance to respond, for Magnussen heard the whispering and stalked across the deck. Engulfed in the scent of Magnussen’s expensive cologne, John was helpless to move when Magnussen cupped the underside of his jaw. The crewmen shifted uncomfortably and a hot coil of shame uncurled in John’s gut. This touch was nothing like Sherlock’s.

Magnussen studied John’s face. He let his thumb press gently into the thin skin below John’s eye.

“You will keelhaul me,” John forced himself to stare straight into those inscrutable eyes.

“Yes,” Magnussen confirmed. His gaze dropped to John’s lips. “There should be sufficient activity to attract the attention of any _sirens_ in these waters.”

“You're mad.”

A muscle in Magnussen’s cheek twitched. “Your opinion is not necessary, my dear sir: only your blood.”

Magnussen’s hand fell from his cheek, thumb catching briefly on John’s lower lip as he plucked Olizarat’s tooth from around his neck.

“NO!”

“Shhh. If I were the kind of man who believed in destiny, I might say that this is your purpose. Your _raison d’etre._ It’s a shame your story ends here, but take comfort in the knowledge that your life won’t go to waste. Why, I shall devote a whole paragraph to your noble sacrifice in my paper. Good-bye, John Watson.”

The crew shoved John’s shoulders and sent him toppling head-over-heels off the deck of the _Appledore_ and into the Mediterranean sea.

The sensation of falling backwards was sickening. John’s stomach was in his throat and there was no room for it. His vision came in three stages: a whirl of cotton-white clouds, the black jutting rocks of Sherlock’s grotto, and then turquoise ocean. The impact was terrible.

With arms and legs bound, John was helpless. The breath was punched from his lungs. As the water closed over his head, he found himself thinking, rather absurdly:

_I’ve..._

_I’ve always loved the ocean._

The rope around his ankles went taut and John was dragged feet-first and fast under the thick curve of the _Appledore_ ’s belly. A cascade of bubbles spiraled in his wake. The woodgrain was gritty against his front, grating his torso. He turned his face to the side to preserve his nose, but his head still clunked painfully against wood. This portion of the hull was, thankfully, sparsely adorned with barnacles - but John knew the deeper he was dragged, the more likely it would be that he would strike them.

Sure enough, he felt the moment he struck the first barnacle. It was as though a razor-edged spoon was removing a scoop of flesh from his calf. If John had had any air left, he would have wasted it by screaming. There was nothing logical left in him. The bright spot of pain in his leg, the wicked scrape of the _Appledore’_ s hull, and the pulsing squeeze of his bereft lungs all combined to turn John small and stupid with agony.

John squeezed his eyes shut and braced against the torment as best he could, bouncing off of the belly of the ship going down, down, down.

Then he felt a sudden pressure against his shoulders and heard a thud underwater. John’s eyes flew open, and Sherlock’s face was upside-down and right by his - looking as feral as John had ever seen him. If John hadn’t been at a deficit of oxygen, he might have gasped. Sherlock's pupils had flattened into their characteristic cuttlefish squiggle. His hair danced underwater like a black candle’s flame and light from the surface flickered off his scales. He had flung himself bodily between John and the hull, acting as a physical barrier to prevent John from being raked.

_No! Your fins!_

The undine met John’s panicked gaze and let out a harsh click. For a moment John thought that Sherlock was going to tear him to pieces, so frightful was the dark energy vibrating through the merman’s enormous body. Instead, he pushed down on John’s shoulders and swam downward away from the hull. A cloud of red blossomed in the water when his dorsal fin snagged upon a cluster of barnacles. John’s body spasmed, desperate for breath.

Sherlock’s gaze flicked calculatingly from John to rope that still tethered him to the ship. His body coiled in the the water until he was quite upside-down. Grimacing, he took the rope that tethered John to the ship and tore it clean in two. It was a feat of strength that John would have said was impossible, but when it came to Sherlock - well. ‘Impossible’ seemed terribly unimaginative.

John couldn't fight the urge to inhale much longer and he was glad when Sherlock dragged him to the surface. John spluttered and wondered precisely how many times, now, he’d been near-drowned. His body stung, unpredictable constellations of pain winking on and off as Sherlock spun him like a teetotum in order to peel the heavy rope away.

“S-Sherlock, I --” John coughed out seawater and what he strongly suspected was a small fish.

Sherlock dipped below to shuck the rope from John’s ankles and emerged glowering.

“Listen --” John began again.

“Foolish human. I should have eaten you when I had the chance. You would leave me! _ME!”_ Sherlock’s eyes were wild, curls clinging wetly to the curve of his cheekbones as the ocean lapped at his chin.

John snorted out seawater from a poorly-timed wave. He found it difficult to swim of his own power for he was still short of breath. “You’re in danger!”

“NO, John Watson. _You’re_ in danger,” growled Sherlock, his voice thunder-deep. “See how your own kind tries to kill you! You must get away from here. Go to mine own nest. Hide.”

“No, no, _no!_ I am just the bait! It’s _you_ he wants.”

“Oi! Look ‘ere!” came a faint shout from above. They looked up.

Leaning over the bulwark were Magnussen and the majority of his small crew. The expressions on the crewmen’s faces were singular. Magnussen was squinting between Sherlock and John with unabashed fascination. It was as though he couldn’t decide which was more fascinating - the sudden appearance of a _greater siren_ or the fact that it had very obviously rescued the bait.

John cursed. “Sherlock, please! I’m begging you, for the love of god you must flee. He has a machine.”

“A what? I will not go, John. You can barely swim.”

A cacophony of sound erupted aboard the _Appledore_. A flurry of footsteps, the sound of wheels on wood, and the squeak of metal springs followed by pulsing gushes of air. John pushed fruitlessly at Sherlock. The undine’s throat quivered, gills flared open with what John recognized to be the precursor to a Song.

Then it happened. Magnussen activated his machine.

John felt it in his bones more than he actually heard it, for the sound was outside of human range - a faint buzz that was easily ignored. The effect it had on Sherlock, though, was instantaneous and terrible. Sherlock convulsed in the water. His tail thrashed about wildly, stiff and uncoordinated, fins flared to fullest capacity and tangling around each other. His face stretched in a silent scream.

“Sherlock!” cried John, battered back by the turbulence of Sherlock’s convulsions. “Oh, god, _no_!”

“Prepare the net! We’ve only got one shot at this, boys, make it count.”

The rigged wooden beam swung out above the water. The sun glinted off of a huge metal net and the pulley system that accompanied it. It was quite beyond John’s capability to swim through the turbulence and reach Sherlock at this time - but still he tried. Sherlock’s eyes were marbles of white, the color lost somewhere behind shivering lids.

John prayed for a serendipitous bolt of lightning to strike Magnussen dead.

“LET ‘ER DROP!”

The net fell into the water, and it was terrible to see how quickly Sherlock became entangled. His fins were a maelstrom of white that in the cruel metal trappings. John was helpless to do anything but look on in horror as Sherlock’s spasms further immobilized him.

“REEL ‘IM IN!”

Although the _Appledore’s_ bow dipped slightly with the weight, the pulley system held. Water rained down as Sherlock was hauled clean out of the ocean. Spinning slowly in the sky he seemed larger than life, writhing in the net and mouth open in a silent scream. John couldn’t see the crew, but he could hear their frantic footfalls on deck, their excited chatter and exclamations. John struggled to get close to the ship without becoming sucked under. He had to help Sherlock. But Magnussen’s head appeared over the bulwark, followed by the gleaming muzzle of the rifle. He scouted the water until he spotted John.

“Well, well, well. This specimen’s a beauty, isn’t it?" Magnussen gloated. “You, my duplicitous friend, are almost a greater mystery than the _siren_ itself. I’ll have the truth now, if you please.”

“Turn off the blasted machine. Let him go,” gasped John, wishing he had the breath to shout. His demand was further undermined by the fact that a wave slapped him in the face mid-sentence.

Magnussen glared, adjusting his position on deck in order to keep John in his line of sight as the _Appledore_ swung wide. “I shall not. Tell me why this creature saved you.”

John windmilled his arms to stay afloat in an ocean stained pink with his own blood. The sun was blinding over the water, the saltwater stung his wounds, and he wished that Magnussen was within striking range. When it became apparent that information was not forthcoming, Magnussen’s gaze darkened.

“Very well. Take your secrets with you... to the grave. But know this; the _siren_ is mine now.”

The _Appledore_ caught her wind, then, and suddenly leapt forward. Even from the ocean John could hear the pattering of the crew’s feet as they set about to change course. Recognizing that he would be run down if he didn’t move, and most likely shot if he tried to climb the cargo netting, John made haste to get out of the way. The net rattled and shook with Sherlock’s unpredictable jerking.

The _Appledore_ , with the undine suspended high above the waves, sailed away.

~  ~

The smaller the ship got, the fainter the noise of Magnussen’s odious machine became until at last the only sound was susurrus of the waves. John was a bundle of raw nerves. His mind felt like a hollow gourd, the single seed of Magnussen’s last words rattling loudly inside his head: ‘ _The siren is mine now_.’

Oddly, his body seemed to have adapted to the pain, or perhaps the buzzing in his blood shielded him from experiencing it properly. He stared unseeing out to sea. Although it didn’t hurt, John had struck his head on the hull and blood tried in a sticky sheet down the side of his face, clumping his lashes. He was glad of the linen trousers he’d stolen from the skeleton of Algernon Portnay Kirk. They had protected his thighs and groin. He did flinch, however, when his fingertips caught over his right pectoral. One of his nipples had been sheared off.

‘ _The siren is mine, now.’_

John floated in a haze. On the one hand, he could give in to despair. He could lie back on the waves and float until he recuperated enough to attempt the swim back to the island and take his chances with the sharks that were no doubt congregating below. On the other hand...

‘ _The siren is mine, now.’_

He looked skyward and checked the position of the sun. He looked back at Sherlock’s island. Back to the sun. His fingers drifted to his neck, which felt barren without the weight of the leviathan’s tooth.

John muttered aloud, “You can sleep when you’re dead, old boy.”

So he began to swim at a conservative pace, for he only had one chance - his accuracy must not falter. He did not swim back toward the island, and he did not swim after the _Appledore_.

Ten minutes or so must have passed in strained silence, when a shark appeared in the clear water. _Blast. I don’t have time for this. It’s not even a Named One._

John waited until it darted in close, and then punched it with all the force he could muster. Stunned, the shark floated stiffly away and made no further attempt to harangue him. For the rest of its days, that shark never approached any other two-legs it smelled, no matter how much blood was in the water. It passed down warnings to its offspring. To this day, there lives in the Mediterranean sea an entire line of sharks that refuse to partake of man’s flesh, all thanks to John Watson.

He resumed his journey tiredly.

Presently, a familiar spiny fluke popped up above the waves alongside him. John thought it was another shark and his bruised knuckles throbbed in anticipation, but it was just Mycroft. The undine lifted his head out of the water to regard him with furrowed brow.

“John Watson. I couldn’t get close to the human ship. There is a terrible sound - I can still hear it, on the distant winds. Where is mine own brother?”

"I know. That sound is designed to impede your kind,” John said. He blew out water. “As for Sherlock, he's alive but they - they took him.”

"I knew it," said Mycroft. His tone was carefully devoid of emotion. A pause. Then, “Land is back that way.”

John didn't dignify that with a response. He had eyes. He focused on pushing through the shriek of his tired muscles and the knifeish pain of where his right nipple had been. It was almost comical how easily Mycroft kept pace with him - how clumsy and ill-adapted John was in comparison.

"You are going the wrong way," Mycroft sounded perplexed. His voice sounded distant to John. Tinny. "And you are wounded."

John’s arms gave out. He began to sink.

The ocean closed over his face and the sun shone through the ripples as a blurred white disc. John reached for the sun. The light shone through his skin, turning his fingertips vibrant red at the tips. 'The siren is mine, now,' said Magnussen's voice, and this time he sounded delighted.

Mycroft's shadow eclipsed the light. He took John's hand. 

John sagged like wet tissue paper as he was drawn back to the surface. His arms and legs hung like lead weights and his head fell to the crook of Mycroft’s neck. Mycroft’s gills fluttered in embarrassment at the proximity - but the slow rock of his tail didn’t falter. John closed his eyes. He couldn’t seem to stop shaking. Inhale. Exhale. Inhale. A cacophonous feeling expanded in John’s chest and fanned out until it burst from his lips as a sob.

Mycroft froze.

Aside from that first sob he was too slow to choke back, John wept in stoic silence. It felt good. Cathartic. In that moment, crying felt more necessary to him than breathing, or drinking, eating - a basic need he had too long neglected, at last tended to. The ocean lapped away his tears and he recalled how Sherlock had wanted to know why humans wept. Mycroft lacked his brother’s curiosity and held himself in a rictus of discomfort. He went to pat John’s head, but second guessed himself. His hand hovered awkwardly over John’s shoulder.

“This is all my fault," John told Mycroft’s neck gills.

"This is not the first time that this human ship has come into mine own brother’s territory. I warned him many moons ago it had returned. Mine own brother knew the risks."

John watched the fanlike ripple of Mycroft’s dorsal spines beneath the water. If he grabbed one, would the venom kill him? This macabre thought jostled him. _Get it together, Watson! You morose, useless lump. What does floating here weeping accomplish? How do your tears liberate the one you love?_

“Right. That’s enough of that,” John told himself rather too loudly. He scrubbed his hand over his face briskly, evidence of his despair gone fast as a summer shower. He pushed off of Mycroft and willed his limbs to move. Eventually, he would get there. Eventually, he would --

"What are you  _doing_?” Mycroft asked in astonishment.

John replied tersely, “He took Sherlock from me. He can’t have him.”

Mycroft swam into his path. He sounded befuddled. “So you are going after the ship alone? John, you are not even going in the right direction.”

John slapped the water. Pain lanced up through his pectoral where his nipple had been. “I may not be bloody undine, but if there is one thing on God’s green earth that I _can_ do, it’s navigate. At. SEA. I’m going to the islet where Sherlock keeps his skeleton, and buried treasure. Why don’t you put your damned wave weaving to use and help me get there, eh?”

Mycroft’s eyebrows disappeared into his wet hairline.

“Well?” demanded John. His patience was utterly spent. “Either you can make yourself useful and help me, or get out of my way.”

Mycroft's mildly incredulous expression had now transformed into an outright gape.

“USELESS!” John bellowed and turned right into the waves that seemed dead set on undermining his progress. As he muscled past Mycroft, the undine took his arm. There was power in that grip, and he was reminded that Mycroft was possessed of supernatural strength - it was possible the only reason he had, thus far, tolerated John's brusqueness was because it was akin to a mouse threatening a housecat. But Mycroft did not hurt him. Instead, John felt the water swell with some supernatural energy, and then Mycroft began to tow him.

After a moment, Mycroft ventured cautiously: “... Sherlock has buried treasure?”

John laughed despite himself. “He does. It’s unbelievable. But that’s not why I’m going there.”

“Why are you going there?”

“There’s a dinghy. I need it if I’m to catch up to them - no, no, don’t stop swimming. Damnit Mycroft!”

“John, humans are dangerous _._ See how they have wounded you already. They will kill you, and mine own brother both.”

“Humans _are_ dangerous, Mycroft,” John agreed, tightening his grip on the undine’s slippery forearm. “I am not letting them take Sherlock. You’re going to help me get back to the _Appledore -_ or at least, as close as you can come. I’ll take care of the rest. After all…”

There. In the distance, the islet of bone.

John smiled grimly.

“I’m human, too.”

**Notes for the Chapter:**

> I am so exhausted, I need to go sleep for a million years now. Please go explore [the blog](http://jinglebellfic.tumblr.com/tagged/riptide-lover) if you have questions about this story, want to see the incredible fanworks inspired by it, or just want to say hi. Words of encouragement would be particularly welcome, as I am now at the part of the story as a creator in which I'm running on stamina and spitfire!


	17. Charybdis

**Notes for the Chapter:**

> I did it. I wrote the thing. I am so happy to share this chapter, because it gave me a lot of difficulty! My sincerest gratitude to the Antidiogenes Club for keeping me on task during word wars, [Catie-Brie](http://archiveofourown.org/users/CatieBrie/works) for her endless patience, Oulfis for his wonderful help, and my esteemed beta -- or should I say alpha? haha! -- [Redscudery](http://archiveofourown.org/users/redscudery/pseuds/redscudery/works). Who is a stunning writer. Thanks to Craig for consulting on mechanics. Friends, please mind the tags and brace yourself for murderous chaos on the high seas. I know you’ve all been waiting, so without further adieu..!

_“Yea, and if some god shall wreck me in the wine-dark deep,_

_even so I will endure… for already I have suffered full much,_

_and much have I toiled in perils of waves and war.” - Homer, The Odyssey_

~  ~

As a sailor, John had learned to read the motion of the water the way another man might read a map. He would never feel half as competent as he did with a spangled sky above and a sturdy deck below -- but the view from atop a boat was very different from the view whilst swimming. 

Mycroft, John decided, was none so bad for a man-eating fish. 

The undine had proven himself invaluable by helping John get to the islet of bone where Sherlock hoarded his treasured human skeleton. John was relieved to see that the dinghy he recalled was still there on the beach. The vessel did have weather damage; there was a crack on one of the gunwales. Since it didn’t extend to the waterline, he was optimistic. 

Using one of the oars, John emptied most of the sand from the half-buried boat and pushed it down the slope to the sea. It dipped ominously in the shallows. John held his breath, but it bobbed back up again. 

"Hm. It actually floats,” remarked Mycroft. His blue eyes were fever-bright. He seemed reluctant to look away from John.

“Of course it floats,” John retorted. He turned away from that searing gaze. “Now, see here. I’ve never heard of a rowboat catching up to a clipper. In fact… I’d say it’s impossible.”

Mycroft reared out of the water somewhat, exposing his striped torso. In direct sunlight, the color of his stripes seemed more arterial red than burgundy. He gripped a webbed hand over the gunwale and pushed down to test the buoyancy. “For a human alone it may be impossible. If this boat does not break, catching up to the humans won’t be a problem."

"Won't it? Do you intend to move this, then?" John asked innocently.

"Yes.”

“If luck smiles upon us, we’ll find that clipper.” _But never mind catching up with her -- how shall we find the Appledore to begin with? I should think it will be the greatest test of my abilities as a mariner._

Mycroft’s aural fins flexed in an undine sneer. “Only a fool relies on luck, John Watson."

"Then I'm a fool," John said. He mopped at the blood on his chest with one hand and checked the viability of the rowlocks with the other. "And foolishly, I will rescue Sherlock, if it’s the last thing I do.”

Mycroft’s gills flexed open. "I know where the human ship is.”

John did a double-take. 

“Sound travels well in the beneath. While you were digging out this improbable little ship, I listened for the hateful noise.”

“You can hear Magnussen’s machine from this distance?” 

Mycroft blinked. His nictitating membranes slid briefly over his eyes. “Locating mine own brother will not be a problem, provided this vessel doesn’t sink. But if I venture too close I expect I shall become incapacitated.”

"No, no, there’ll be none of that. Leave the machine to me. I will find a way to silence it."

"I hope you will," confessed Mycroft. His gills fluttered and he gave John his beaky profile. He plucked at a bit of floating detritus. 

“We’ll get him back. Right. Well. Let me just -- I’ll, that is, I’ll see if there’s anything useful left before we set off.”

The flat boulder was as John had left it weeks ago. He recalled the afternoon spent swimming with the dolphins. Sherlock’s skin had felt slippery-firm, catching slightly on John’s callused fingertips. _God_. He would give anything just to touch Sherlock’s skin again. _Focus, old boy_. He dragged the boulder aside. John unlatched the lid and reached around Algernon Portnay Kirk to rifle through the gleaming pile of ingots, cut gems, and Sicilian dollars until his fingers curled around the prize he sought. 

“What is that?” Mycroft asked, steadying the dinghy as John sloshed into the shallows, threw a leg over, and fell in. There was uncomfortable moment when the vessel dipped and bobbed, but she held.

“Booze.” John popped the cork with his teeth and spat it into the sea. The smell that wafted from that dusty old bottle made his nose hair curl and seared a stripe of optimism down his sternum. He planted himself on the thwart with the bottle sandwiched between his thighs and took up the oars. “Let’s see what this old girl is capable of.”

“Allow me,” Mycroft said with all the grace of a gentleman asking a lady to dance, and his pupils slowly contracted. The water furled open like a sheet over a mattress. The rolling waves swept the dinghy away from the islet and out to the open sea. For all intents and purposes, it appeared as though the rowboat was surging along of its own power -- an odd sight appreciated by no one but the gulls and Mycroft.

John was struck by loneliness. The sunset turned the waves into glittering fool’s gold, but the beauty of the seascape served only as a bleak reminder that time was running out. He spoke aloud to the sleek head peeping out of the waves in front of the boat. “It’s all gone to hell, Mycroft. It’s just all gone to hell.” 

He chugged the antediluvian booze.

John had had the stuffing beaten out of him belowdecks in clandestine fights. He’d lost a molar and he’d lost his dignity. Bruises, John thought, would be preferable to the sting of countless tiny abrasions from his aborted keelhauling. But the ache of his body was insufficient to distract him from the ache of his heart. How had it come to this?

John had every reason to expect the worst. What if he was already too late? What if Mycroft had overestimated his ability to catch them up to the _Appledore_? The clipper, and its precious cargo, could be at an irreconcilable distance. They could be completely wrong about where the _Appledore_ even was. Certainly, Mycroft seemed cool and confident as always -- but when would an undine admit weakness? Perhaps Mycroft was only confident because the alternative was despair.

Which made John ponder whether an undine could even feel grief in the same way a man could. What would he do if he lost Sherlock forever? What would it be like to return to London months too late? To arrive just in time to read the breaking news of Sherlock’s dissection in the papers? What did John really have left but that damned undine? He certainly couldn’t collect a paycheck from the HMS Endymion. If the ship made it back to Deptford port in one piece, a list of those lost at sea would have been compiled for the families.

Harriet probably thought John was dead. 

There was nothing left for him in London, and London was not, would _never_ be, ready for Sherlock. John’s fists clenched in his lap. He wanted to hit something. He wanted to squeeze Magnussen’s neck until the madman learned to value simple things like air over collecting specimens. He wished he could row the dinghy himself, because at least then he would be taking some kind of action.

Nothing could soothe his nebulous anxiety. He could only worry, and drink, and then worry some more.  

After an hour’s worth of travel, the dinghy slowed. The supernatural tension that had been thrumming through the floorboards faded away and John frowned. He leaned over the edge.

“Mycroft?”

What he saw froze his blood. Mycroft’s face floated just inches beneath the surface; his pupils were fully contracted into the w-shaped squiggle that, when observed in Sherlock, meant a feral episode was well underway. His lionfish tail swayed below, the flat blades of his venomous spines flared out. 

A single drop of blood beaded on John’s chest and hung suspended between them. _Plip_. The dot of red landed in the sea and blossomed out before the waves dispersed it. Mycroft's face changed, no longer the visage of a stodgy vicar or some minor government official, but something sharp. There was nothing harmless about the way he licked his pointed teeth.

John had enough foresight to scramble back the moment before Mycroft breached in a colossal crash of waves. 

The dinghy was not meant to hold such weight and sank a full foot under Mycroft’s bulk as he pulled himself up the pitching thwart toward John, who balanced at the breasthook shouting. Mycroft’s hiss was more ocean than animal. His head was nearly at John’s toes where they curled into the ribs of the boat, and John wished he was anywhere but where he was. _I forgot. I forgot how dangerous he is, underneath his civil words. How could I forget?_

Water burbled up around them and the boat tipped drastically -- John had to cling for dear life and pray that it didn’t sink. If he was tossed into the ocean with Mycroft in this state, the undine would be upon him.

“Mycroft,” John gasped around the weight of his heart lodged in his throat. “Mycroft, look at me. Up here.”

He felt cool breath on his bleeding calf, followed by the slick touch of an inquisitorial tongue against the largest wound. John swallowed and squeezed his eyes shut. 

“The dinghy cannot hold both of us. If -- if you eat me, you will never be able to save Sherlock. Don’t you want to save Sherlock? Your brother?”

The hissing stopped. 

John pressed his advantage. “Sherlock needs us. But you can’t get close to the ship without my help. Kill me now, and you will never see your brother again. Mycroft, please.”

The dinghy shifted catastrophically as the undine slithered slowly back into the water. John lay in several inches of seawater and panted. He still wasn’t entirely sure the dinghy wasn’t going under.

“John?” came a quiet voice on the other side of the bulwark.

He did not reply.

“John?” the voice was a little louder now. Strained.

“Yes?” 

“My apologies.” 

John said nothing.

“I don’t know what came over me. I usually have, ah, better control. The wave weaving is strenuous, and I -- well. Never mind that.”

John watched the bruise-colored clouds float by in silence. His ears were ringing.

“John? Please come out.”

John scrubbed his hand over his face. He sat up slowly, gazing through the crack in his fingers at where Mycroft floated nearby. He had preened his hair back into place and smoothed his gills as though nothing had ever happened. He was watching John.  “As you said. My brother needs us. Shall we?”

John nodded.

~  ~

And so it went that John and Mycroft commenced their rescue mission, in the inauspicious summer of 1866. The sea was clear for miles ahead and along they hurtled, a creaky wooden bullet. The wind whipped back John’s hair. He found himself squinting, for the full moon was ungodly bright and brought the seascape into high contrast. He heard the drone of the machine before he spotted the clipper at last. 

There.

Sherlock was on that ship.

“You’re up there, my beauty,” John muttered aloud. His hand drifted to the bare spot at his neck where his lucky talismans -- first a bullet, and more recently Olizarat's tooth -- were supposed to be. It was now just naked skin. Vulnerable. “I know you’re hurt, and frightened, and alone. But just hold on, love. I’m coming. I’m coming.”

The waves looked like liquid metal where they slapped up against the _Appledore_ ’s hull. The closer they got to the ship, the tighter Mycroft’s jaw clenched until his teeth began to chatter. When the whites of his eyes started showing, John took over. The ropey muscles of his shoulders bunched and flexed in a long-practiced motion as John rowed himself along. 

He coasted cautiously into the shadow of the ship. The noise of the machine masked John’s thump when he sprang out over the ocean and landed on the cargo netting. The dinghy came close to the ship -- _too close_. _Oh, come on. Float away, float away!_ John willed furiously, and lo! his luck held, and the rowboat drifted away into the night. One crisis averted, John clung to the salt-crusted cargo netting and caught his bearings. His heart slammed, pumping blood warm with Dutch courage. Above, he heard pacing on deck; John waited until the footsteps grew faint, and climbed up to peep over the bulwark. 

Not ten feet away stood the freckled helmsman. A bullseye lantern hung from the rigging, swinging with the motion of the ship and illuminating the man. In the hullabaloo, John hadn’t caught this fellow’s name -- but by the moonlight he recognized the silhouettes of Fletcher, Almonte, and Lestrade working the bellows at the distant prow. Sherlock was an indecipherable mass suspended in the rigging. John inhaled sharply. His first instinct was to rush to Sherlock’s side, but that kind of foolhardiness would get him killed -- John was wounded and outnumbered.

 _I’ll have to get them each alone if I can._ John figured he may as well start with Freckles, since he was already separate from the rest of the crew. The little bloke was steady on the wheel. John stumbled over the bulwark. He froze, cursing his exhaustion -- but the helmsman didn’t react at all. _By Jove, the boy must be deaf as a post!_  John made a club of his fists and clocked Freckles on the back of the head. He went down, and John caught him under the arms that he might lower him quietly to the deck. He assured himself that the man was breathing, and in so doing discovered that Freckles had plugged his ears with rolls of white linen. Now _there_ was something. If all of the crew had so little patience for the sound of Magnussen’s machine, it would work to his advantage. 

John stepped carefully, carefully over the helmsman’s prone form and steadied the helm. He relied on the night to obfuscate his identity; best to hide in plain sight. If any of the crewman glanced aft they would be more likely to raise the alarm were a figure absent at the wheel. 

Through the ratlines and standing rigging, Sherlock hung so close, and yet so damned far away. It was impossible to see the undine’s face from here, but his plumage was bunched around the Gordian knot of his tail, and his hair was an absolute mess. John’s heart squeezed -- just how long had Sherlock been convulsing? How could these men watch as Sherlock writhed until exhaustion stilled him? 

The winds changed, blowing a gust of faint conversation across the deck and to John’s ears:

“Ugh, this damned machine. I can hear it even through my earplugs,” said a nasal voice. Almonte, John guessed. “How can you stand it? Can’t we turn it off for just a moment?” 

Lestrade shook his head emphatically as he worked the bellows. “I don’t like to put things in my ears. And no, we can’t. Not unless you want this fellow to wake up and raise hell.” 

“What?”

“I said, not unless you want this fellow to wake up and raise hell.”

“Tsk! Look at it. It gave up the ghost an hour ago. It’s half dead now, Lestrade, and if you ask me it’ll be full dead before we reach Valletta, let alone London. This beast is harmless now,” Almonte grunted, leaning over to check a brass instrument.

The wind changed again, and the conversation was lost to John. He contemplated moving closer, but Almonte strutted over to stand below Sherlock. He paced beneath the undine, cold as a Roman soldier at the crucifixion. He tugged on an exposed ruffle of caudal fin where it stuck out of the netting. 

Sherlock did not so much as twitch.

“Tch. It was more exciting when he was floundering about,” groused Fletcher, who was watching the proceedings whilst monitoring the cables. Encouraged by the sight of someone else touching the monster, Fletcher reached up and carded his fingers through Sherlock’s frizzled curls. 

John saw red. Propelled by the the drink, he leapt down the quarterdeck stairs and was halfway to the forecastle, projecting his voice across deck: “Right. That’s enough of that, then.”

Almonte shrieked. Fletcher jerked his hand back as though he had been burnt. Lestrade stiffened but did not release the bellows. There was a momentary kerfuffle in which everyone tried to locate the source of John’s voice before simultaneously understanding that he was, in fact, mere feet from them on the deck. Then there was another moment while everyone took in his appearance. 

John was half naked, covered in bloodied scrapes, and not keen on diplomacy. His wet feet slapped the deck as he charged Fletcher, who had the misfortune of being closest. They crashed into the bulwark. Fletcher’s head cracked against the wood and he crumpled onto the deck, stunned; John dropped him and whirled to address Almonte's rapid footfalls. He engaged John with utility knife drawn. 

Almonte slashed low and John seized his wrist. John twisted his arm, and the knife clattered to the deck.

“You’ll be releasing Sherlock now,” he commanded. Almonte did not reply with the anticipated immediacy, so John gave him a little shake. “You’d best not call for your master.”

Almonte whimpered. “You’re mad. How did you even get on board?! We left you hours ago in the middle of the bloody ocean!”

“He followed us on a dinghy somehow,” Lestrade said loudly over the noise of the machine. He was squinting, a fine sheen of sweat on his brow. “Ask me how I know.”

Oddly, it was Almonte who snapped: “How do you figure that?” 

“Because Dodson is leaving in it.”

Everyone looked out to sea. It appeared the helmsman had regained consciousness, spotted the drifting dinghy, and promptly jumped ship. This sight inspired a renewed ferocity in Almonte, who broke free of John’s grip with a feverish grunt.

“Devil take the lot of you. I’m going with him!” Almonte leapt overboard. A distant splash marked his egress. John and Lestrade glanced at each other, wide-eyed.

“Well,” Lestrade said slowly. “I didn’t like ‘im much, anyway.”

John latched onto this promising show of conviviality, although his tone came out sharp with anger and stress. “Lestrade, please. You must stop pumping those bellows.”

“What, asking nicely now? Why not just crack my head like you did Fletcher there?” 

John glanced at where the crewman in question clutched his head dazedly. Though conscious, Fletcher clearly was not inclined to get up yet. _He touched Sherlock, condoned his torment,_ John thought with a little spike of anger. _He deserved that and then some._

Lestrade continued. “If I stop, Magnussen will come up to see what happened. It’s the same as me calling for ‘im right now. I really should call ‘im.” 

“If you were going to do that, you would have done it already. You’re curious about me. You want to know how I survived on the island, yeah?”

Lestrade frowned but John pressed. “I’ll tell you. I’ll tell you the truth, the truth I won’t tell Magnussen -- but right now there isn’t time. Sherlock is too heavy for me to carry alone. Help me return him to the sea.”

Lestrade's lips thinned, but he inclined his head slightly whilst metronomically pumping. His tone was dry. "Got a name, does he?"

Although he would never have admitted this sober, John was still feeling the effects of the booze he had imbibed in pursuit. It was with absolutely no forethought that he confessed: “Yes. His name is Sherlock, and he is the best and brightest person I have ever known, and he is mine.”

John flushed as Lestrade's eyebrows disappeared into his hairline.

“If you’re lookin’ for a disagreement you won’t find it with me,” Lestrade said frankly. “You did find the _greater siren_ before Magnussen.”

 _He thinks it rankles that Magnussen would take the credit for this discovery_ , John realized. Here was an opportunity to agree, handed to him on a silver platter. No one was holding a gun to John’s temple, no one was forcing him to confess anything, and yet… the truth was boiling inside of him. Lestrade was a blackmailed sailor, enmired in a predicament nearly as unfortunate as John’s. 

If not now, then when? 

“You… misunderstand,” John said quietly.

Lestrade looked at him.

“I -- ah. I love him.”

Lestrade’s eyes grew as large as saucers. He nearly dropped the handles of the bellows -- the first time John had seen him falter at his task. Wood-brown eyes flicked rapidly over John’s face, seeking the joke.

A long moment passed.

A very, very long moment. 

It must have been the longest moment in the history of the world, for John felt greatly aged by the time Lestrade cleared his throat and whispered, “... and I thought I had problems, mate.”

“Please. You can’t take him away from here. Magnussen will kill him eventually, one way or another. I won’t stand for it. He won’t survive in the city, and I think that fellow was right -- at this rate he won’t even live to see Deptford. Look at him, Lestrade. For pity’s sake!”

Lestrade hesitated. 

He tore his eyes from John’s face. He looked at Sherlock, who did in fact cut a tragic picture. Then John’s heart sank a little, because Lestrade’s gaze drifted back to where Fletcher lay stunned.

“I don’t want to hurt anyone else. Please, you must believe me. But I must get Sherlock back into the sea before he dries out, before he dies. What you’re doing, you. You are kidnapping a man. He is as human as you or I.”

Lestrade’s pumping slowed, and the drone of the machine took on a sluggish pitch. “John, I… I don’t know what to say. Magnussen’s got my daughter’s reputation in the palm of ‘is hand, see. I never wanted to be here but I fear for her life, ‘er reputation. And I can’t tell which of these boys are blackmailed and which are loyal to him! I just don’t know.”

"How much longer are you going to let him control you?" John snarled.

Lestrade looked away. John stepped closer and carefully clasped Lestrade’s upper arm. "You have a choice, you know. You always have a choice. And Sherlock doesn't deserve this." As the words came out John realized the truth of them, and the irony of this latent realization wasn't lost on him. John willed the other man to see him, to understand. Sherlock would _die_. That was a crime against nature, for there was no other being alive quite like Sherlock. Time was running out. 

Lestrade sighed. He looked down at the thin metal handles. His gaze lingered on the cut on his forearm where John had nicked him earlier. John’s heart sank. _Damn. He won’t help me, then. Don’t know what I was thinking, telling a near stranger all of that -- why should he care? He’s like me, before all of this. He looks at Sherlock and he sees a monster, as inhuman as it gets. He couldn’t possibly understand how I feel, and even if he did, what could he do? Every man has his own troubles, Watson, and every man’s for himself. You old fool._

“To hell with it.” Lestrade spoke in a single exhalation. He seemed almost surprised by the words that came out of his own mouth: “Do you know, that’s the first _compassionate_ thing I’ve heard on this thrice-damned quest? Devil take Magnussen. The villain’s a blackmailer, and not a one of us has the stones to oppose him.” Lestrade looked up with a manic smile.  “John. Quickly now. He’ll come up the moment he hears his machine is undone! Start with the knot over the winch on that boom. We’ve got to get your lad on the deck before we can open the net.”

In that moment John’s heart was a cloud. With an ear-splitting grin, he sprang to the boom and began to pluck away at the knot until the rope slackened. Sherlock slid to the deck with a thump that actually rocked the _Appledore_. Lestrade released the handles. The machine sputtered and died.

John skidded on his knees in his haste to come to Sherlock’s side. The undine was terribly entangled, and terribly cold to the touch. It was the first time John would describe Sherlock as feeling like -- well, a dead fish. It felt wrong. John lifted his head into his lap, bending over to touch their foreheads together. The thin metal bars between them felt like lines of ice against his brow.

“Sherlock, c’mon now. Time to go.” 

Sherlock’s eyelids shivered but did not open. Now that Sherlock was in his arms once more, the last thing John wanted to do was let him go -- but he needed to help with the Herculean task of untangling the undine’s knotted caudal fins from the net. So he pressed a chapped kiss on Sherlock’s brow and joined Lestrade where he was working open the mouth of the net. 

Every metallic clink seemed designed to summon Magnussen above deck.

Sherlock was partially untangled when Fletcher once more made his presence known. He swerved to his feet with the utility knife in hand. “Lestrade, you god-damned traitor! You might be willing to risk your daughter, but it’s my neck on the line. Magnussen ain’t gonna catch me mutinizing.”

He came at John, but didn’t account for the strength of Lestrade’s newfound resolution. The muffled grunts and thumps of the ensuing altercation seemed especially loud without the mechanical drone muffling them. _Damn._ John turned back to his task with hands steady as bedrock. If he rushed, he might rip Sherlock’s plumage. 

Inch by rubbery inch, he carefully teased Sherlock’s fins free of the net -- but his luck didn’t hold. Lestrade cried out, and then John heard rapid footfalls. His instinct was the leap aside, but in so doing he might expose Sherlock to the knife: so John whirled around and threw up his arms. 

Fletcher cut John’s forearm, a whip of crimson spattering on deck.

“F-fecking freak of nature, s’what you are. I heard what you said, you beast-loving arse bandit!” Fletcher slashed, quick and brutal with the sharp side of the knife, and John could do naught but grit his teeth and scuttle sideways like a crab, hoping to lure Fletcher away from Sherlock. It worked. Fletcher pursued him across the deck -- or he might have, had his neck not suddenly snapped back. 

For a moment John honestly hadn’t the foggiest what had happened. 

Sherlock had woken. He snatched Fletcher by his long black hair and yanked him down backwards. The knife went flying. The serpentine lower half of his body was still entangled, but that barely slowed him. John watched in horror as Sherlock buried his face in Fletcher’s neck. It all happened so quickly that John truly couldn’t have stopped the undine even if he had been quick enough to understand. A crimson spray, and Fletcher screamed -- the most terrible, animal sound John had ever heard. 

It was this scream that at last drew Magnussen.

“What the devil is going on?!” snapped Magnussen as he and Omadi jogged briskly up onto deck. 

One could hardly fathom of a worse scene for Magnussen to come upon: the siren was loose, two of his crewmen had abandoned ship, and the marooned sailor he had left to drown was back on his ship and unleashing the siren. With his mess of black hair partially veiling his feral eyes, Sherlock was the embodiment of a nightmare. Magnussen took in the scene in mute disbelief.

The coup de grâce was when Fletcher’s screaming abruptly ended with a wet gurgle. All of the humans, John included, blanched. _Greater siren_ , indeed. 

Something peculiar transpired then. The very moment Fletcher’s screaming stopped, so too did all of the ambient noise of the ocean, the creak of the boat, and even the breath of the men aboard the _Appledore_ that night. The stillness was profound. John cottoned onto what had happened first, and that only made it worse, for he witnessed the precise moment Sherlock realized the consequence of his transgression. 

His eyes widened. 

Sherlock released the body almost gently and shrank in on himself like a vole trying to make itself less obvious to the hawk. He raised his webbed fingers to his lips, feeling the blood there in disbelief. _He’s never known loss_ , John recalled -- but then he felt a rose of pain unfurl in his leg, so sudden and blinding and white-hot that even his scream came out truncated, a startled little bark. 

He perceived the sound of the gunshot itself belatedly.

Struck dumb, John looked up in time to see Magnussen lower his Lindsay single-barrel pistol. The moonlight was unforgiving upon his face, shadowed eyes as black as skull sockets and expression obscured by the dancing smoke. When had he taken aim? 

John looked down at the spread of crimson on his dirty white trouser leg. It had been so fast. 

It had been _so_ fast.

Magnussen clucked in dissatisfaction. He brought the weapon to bear once more and cocked the second hammer. This time he would not miss. 

But at that moment there came on the waves the distant screams of men, and the sound gave them all pause. The screams crescendoed with a rabbit-high shriek whose sudden conclusion turned the duet into a solo of despaired moans, the sounds of a man who knew he was next. Magnussen and his crew turned their attention to the sea, wide-eyed and uncomprehending. 

 _Mycroft_ , John thought dazedly. _Now that the machine is off, Mycroft has come._

In the distracting chaos there was something they had all, even John, forgotten. Not a soul was at the helm. And a ship left unguided will drift. And drift the clipper did, straight onto a hidden reef and from there it ran aground upon a small island. The keel stabbed into the sand and the whole affair jackknifed.

The moon in the Mediterranean sky was bright and beautiful.

~  ~

His mouth was dry. 

His tongue was glued to the roof of his mouth, flavored like metal and ozone. 

A crust of sand and salt sealed his upper and lower lashes together. 

His thigh was numb, his other limbs leaden in a different way. He was afraid to look, afraid to assess the damage -- afraid to see how much time he had left. John lifted his head, his beard heavy with sand, and spat chunks of bloody dirt. His vision was sticky.

_We must have run upon an island. Damn. Sherlock!_

The relentless moonlight carved out silver-lined shapes of the landscape. Wood and bodies were scattered across the beach. Debris from the ocean, cracked pieces of wood, a shattered pane of glass from Magnussen’s machine -- the beach was littered with man-made detritus. 

_How long was I unconscious?_

John squinted at the spindly fingers of the ratlines and rigging of the wrecked clipper, blacker shadows on a black backdrop. Men moaned in the darkness. Blood looked black on the pale sand, and behind them all sagged the ruined silhouette of the _Appledore_.

Sherlock was nowhere to be found. John tried to call for him, his first priority that damned undine -- but dehydration stole his voice. He tried to sit up, but his arms gave out. He hit the sand. _Blast._  

John turned his head to the side and panted against the briny sand. He felt detached from his own body. He wasn’t even certain if he was actually conscious at all, or if his mind had finally cracked. There was movement by his nose: he watched a tiny crab struggle along the churned beach. It scuttled determinedly over the refuse in its path, unstoppable.

John inhaled deeply and lifted himself onto his elbows, shaking like a palsied old dog. With grit teeth he lifted his anvil of a head and took stock.

Magnussen was lying face-up on the beach not ten feet from him.

He was gasping. His glasses were askew. His once-meticulous hair was plastered greasily to his scalp. He was unable to flip onto his front -- for a generous piece of wood from the _Appledore_ ’s artistic keel protruded from his knee, sticking out the other side and funneling a steady stream of blood into the sand beneath him.

White-faced, he looked up at John.

"Watson?! Watson, are you alive?" Lestrade’s voice was faint, coming from somewhere far down the beach. John could barely hear it over the roar of his own blood. He licked his chapped lips. 

"Now, see here!" gasped Magnussen, his voice strained. "I never meant the siren any harm. Be reasonable, John."

John began to crawl. 

"Come now, John. Be reasonable!” Magnussen hissed, eyes darting frantically from side to side, searching for help. 

John didn’t waste his breath replying. When Magnussen saw that John had no intention of slowing down, he attempted to flee. He scrabbled back on hands and arse, dribbling blood from the wooden picket in his knee. John followed the snail trail of blood slowly, focusing on the gleam of Magnussen’s shiny, expensive boots.

“Omadi!?” shouted Magnussen. “Lestrade!!” 

But no one came.

It was, objectively, the saddest and slowest chase in the history of chases. Magnussen splashed straight into a shallow pool, probably only a few inches deep. He stuck there, stymied by the thick seaweed. John caught up. He grabbed Magnussen’s ankle in its too-shiny boot and gritted through a kick in the eye that sent his vision spotty. 

John crawled on top of Magnussen in the tidal pool and they fumbled together. Magnussen dug his thumb into the raw flesh where John’s nipple had been. John grunted and lifted himself onto hands and knees, wheezing aloud in pain at the pressure on his shot leg, his bleeding calf, his body pushed far beyond its limits. He grabbed Magnussen’s face with both hands. He pushed Magnussen’s head down into the rancid water. Magnussen’s arms flailed. John could feel him trying to lift his head, neck muscles stuttering and jumping with the effort. Magnussen’s desperation accelerated and he scratched bloody lines down John’s chest. 

A muscle in John’s cheek jumped and he stared down at where his knuckles blanched white under the water. He felt curiously distant from the experience. Like a cloud floating serenely above a still ocean, watching birds being sucked down into the whirling maw of Charybdis.

_Oh, Nancy Dawson Hi-oh!_

_Cheerly man!_

It was a war of attrition. One of them would have to give up. John refused to relinquish his hold on Magnussen, even though the tidal pool was slowly turning pink with their mixed blood.

_She robbed the bosun Hi-oh!_

_Cheerly man._

Magnussen’s resistance softened. He pawed weakly at John’s throat. John noticed that Olizarat’s tooth -- _John’s_ gift from Sherlock -- was around Magnussen’s neck. Oh, Sherlock.

_That was a caution, Hi-oh!_

_Cheerly, man - O! Haulee, Hi-oh!_

“Die,” John gritted. Magnussen, for once, was obliging. John used the dregs of his energy to slump out of the pool, and then he at last succumbed to the darkness that had been encroaching on his vision. The last thing he saw was the gleam of Olizarat’s tooth in the water.

 _Cheerly man._  

 

**Notes for the Chapter:**

> WHAT WILL HAPPEN NEXT? WILL JOHN SURVIVE? TUNE IN NEXT TIME TO FIND OUT, ON RIPTIDE LOVER ~90's after school anime narrator voice~ Please forgive errors in the fic as I ended up changing some bits last minute and I really prefer to get critique on chapters before I share them -- hence the tardiness -- so my sincerest gratitude to Catie-brie and Oulfis for stepping in for some down to the wire assistance. I am so grateful. 
> 
> There is a TREASURE TROVE of artwork, cosplays, crafts, and creativity folks have shown in the [#Riptide Lover](http://jinglebellfic.tumblr.com/tagged/riptide-lover) tag on my blog, enjoy!


	18. In All My Dreams I Drown

**Summary for the Chapter:**

> Good guy Lestrade and good gal Mrs Hudson make an appearance. Mummy Holmes, of a sort, as well....

**Notes for the Chapter:**

> HI EVERYONE!! This is a turning point in the story, but bear with me. This chapter brought to you by Sweeney Todd. I’m heading to 221b Con next weekend, I'm hoping to squeeze in one more chapter update right before the con. <3 Wish me luck, [check the blog](http://jinglebellfic.tumblr.com/tagged/riptide-lover) or maybe my less-organized [twitter](https://twitter.com/jinglebellfic) for current news. (My fandom twitter will be inundated with convention photos and stuff in about a week, fair warning)
> 
> So much gratitude for the phenomenal [Dr Redscudery](http://archiveofourown.org/users/redscudery/pseuds/redscudery/works), for going through this and all chapters with her fine-toothed comb of a brain. She even did another once-over for me right before her vacation because she has a heart of gold. LOVE YOU, RED <3

The cheery Mediterranean sun filtered through the crack in the drapery and sent a bar of yellow light across John’s body. He stared up at the ceiling of Mrs Hudson’s spare bedroom. The pillow smelled faintly of lye.

Six days.

It had been six days since the altercation. Six days since Magnussen had kidnapped Sherlock. Six days since last he had seen those undine brothers. Six days since John had killed a man. In that time, John had reflected.

Given the state of his leg, he wasn’t capable of much else.

Magnussen’s bullet had, as it turned out, only grazed John’s outer thigh -- but it had taken an impressive chunk of flesh with it. Someday, the scar would heal into a long silvery trench. For now, it merely oozed unmentionable bodily humors and hurt desperately. The wrappings had to be changed every few hours. This task fell to eager, sweet Mrs Martha Hudson.

She was the landlady of the rooming house which he and Lestrade presently occupied. When he had eaten his first proper meal after waking, John had vomited all over the floor. Mrs Hudson tutted sympathetically and insisted that she had been in the market for a new Persian carpet anyway, and he’d rather done her a favor.

Her kindness was more painful than his wound.

A distant part of him thought he ought to be more remorseful about having killed a man, but try as he might, John just couldn’t dredge up any guilt about it. Perhaps living in isolation for so many months had chilled his compassion. His time on Sherlock’s island had fundamentally changed him, and John was still trying to figure out how.

The John of the before, pre-marooned John, might have lain awake plagued by guilt. John of the now, the current John -- well, he lay awake missing Sherlock so deeply that he felt sick with it, feverish and aching and desperate to feel cool skin against his, to hear that subsonic baritone against his throat.

Why waste any more energy thinking about that villain Magnussen? He would have done Sherlock in. Magnussen’s death had made the world a better place. Hadn’t it? John’s thoughts oscillated between defensive numbness and frantic worry, with one star gleaming at the center of it all --

Sherlock.

John’s only thought was for his love, his undine, his own. Never mind his wounds; damn his leg! What had happened to Sherlock? John ground the heel of his hand into his brow and forced himself to recall, in excruciating detail, what took place after the _Appledore_ crashed.

_Overcome with exhaustion, John had collapsed atop Magnussen’s still-warm body._

But... then what?

He drew a blank. Here he must rely on his powers of deduction, for what little they were worth. John had puzzled some things together through a combination of eavesdropping (it was remarkable what people gave away when they thought a man was asleep) and haranguing Lestrade, who had found John collapsed atop of Magnussen’s corpse.  

 

_“And then I heard a noise,” Lestrade had said, a wrinkle appearing between his eyebrows._

_“A noise?” John asked._

_“Yes. It was… like music. But deeper, like the song of a whale and yet, I swear -- Watson you must believe me -- I heard laughter.”_

_‘That sounds like Sherlock’s song,’ John had thought to himself, and for an instant he was overtaken with wild hope. ‘Perhaps Sherlock has not lost his Song after all.’_

  _“It was a merma-- er, an undine,” Lestrade corrected himself with an apologetic glance at John. “The bigger one, with the stripes. Called me over to the water, somehow, with his voice. I went to ‘im.”_

_“Mycroft Sang you,” John said. “He helped me catch up with the Appledore.”_

_“Mycroft? He’s terrifying.”_

_“You’ve got no idea, mate. What happened then?”_

 

John remembered that here Lestrade became coy, despite his indiscreet questioning.

 

_“He told me not to be afraid. Asked after you. I told ‘im I thought you were in bad shape. Told ‘im you’d die unless you got a doctor. And make no mistake, you’d’ve died! Myc… Mycroft did something with the water and the dinghy came right up to shore. S’like a dog answering its master.”_

_Lestrade seemed comforted by John’s earnest expression._

_“So I went and got you quick. There was so much blood... didn’t think you’d make it. Omadi showed up and I thought he’d make trouble, but once he saw Magnussen’d bit it his tune changed. He helped me get you into the boat.”_

 

Omadi had left before John regained consciousness. He’d caught a cargo ship to Nice that very same morning they arrived -- worried about his wife and children, and convinced he had a lead on Magnussen’s moles.

 

_“Magnussen planted men, you know, Watson. To blackmail us with the lives and reputations of those we loved in the event of his death. S’the only reason we didn’t kill ‘im right away, see.”_

_Lestrade’s wood-brown eyes glinted with what John was coming to understand was uncharacteristic vitriol._

_“Gave ‘im a letter to deliver whenever he gets back to London, too. For my daughter. Just want her to know that her old man’s alive, and god willing it’ll arrive before news of Magnussen’s death reaches England.”_

 

This was the part that John had difficulty understanding. If Lestrade’s daughter was in danger, why hadn’t he taken the same ship? It might be weeks before the next Deptford-bound frigate came through port. Lestrade’s answer had surprised and humbled him.

 

_“Oh, make no bones about it, Watson. I thought about it, all the way to the bottom of a bottle of gin. T’be honest m’not sure if it was the gin or my conscience that told me not to abandon a fellow Englishman unconscious and wounded.”_

 

John shoved his face into the pillow to hide his flush from the voyeuristic gaze of Mrs Hudson’s late husband. The oil painting was installed on the wall directly facing the bed.

Lestrade was a rare sort of person in that he was a genuinely good man. Possibly the only one John had come across in years. He was staying in the other bedroom, and was presently paying for their lodging by doing odd jobs for Mrs Hudson, and assisting Angelo at his cookshop in the evenings.

 

_“Anyway, you’ll be wondering about your Sherlock. Mycroft told Omadi and I to take you back here, to ‘the human settlement’. Said he would escort us, but then -- ah, well.”_

_“Say it!” insisted John, expecting the worst._

_“Sherlock saw us leave. Didn’t say much, but it was plain as the nose on my face he didn’t consent to giving you over. Tension ran high, Watson. You were losing a lot of blood. Wasn’t a moment to lose, you must understand. Mycroft -- ah, the big one, told ‘im to stand down… and then Sherlock went at ‘im. Sweet Mary! The noises they made, Watson, I will never forget for the rest of my days. Horrifying sounds._

_“Omadi and I sure as hell weren’t going to wait for them to come back up for tea. We rowed like our lives depended on it, navigated by the stars. By the time we dropped anchor at port it was dawn and the fishmongers were out.”_

_Lestrade cleared his throat uncomfortably. “Anyway, that’s when we met Angelo, buying his fish for the day.”_

 

Angelo was a Sicilian ex-convict and an almost suspiciously kindly cook. He'd come to Malta seeking a new beginning, and after establishing his cookshop met Mrs Martha Hudson who, as it turned out, was looking for tenants to fill the now-empty rooms of her rooming house.

As far as places to recuperate went, one could do worse than Piccola Cala.

It was a tiny coastal town, reminiscent of Valletta with its uneven road infrastructure, long flights of ankle-breaking stairs, and picturesque flat-roofed little houses. The town’s focal point was its docks, sailboats overflowing with the day’s catch. A large sloop was anchored in the bay.

Sherlock and Mycroft had fought. They had fought terribly and John hadn’t been there to calm Sherlock. Mycroft had always wanted him gone, had even offered it to him when they first met. Now that sneaky fish had what he wanted. How could John ever find Sherlock’s island? He had not been conscious for the journey inland. Worse still, John believed that Sherlock could no longer Sing to tell John where he was.

John inhaled sharply.

Sherlock’s Song was gone. John knew this somehow, he knew it like he knew the sun would rise in the morning and set in the evening; he knew it like he knew the ocean tide or the palm of his own hand. How crippled Sherlock must feel, how desperate and alone. He needed John. John was his, his own, and Sherlock was --

Shoes clicked on the uneven hardwood outside John’s door.

“Yoo-hoo! Dearie, may I come in?”

 _No._ “Of course,” John said. Mrs Hudson backed into the room, bearing a tray generous with food.

“Thought I’d bring you a little something. Just this once, mind,” Mrs Hudson told him. Just like she had been saying every morning since he arrived.

“Thank you,” John said. He sat up so that Mrs Hudson could set the tray on his lap.

There was a piece of cold kidney pie and a slice of crusty bread, upon which gleamed a generous layer of butter. There was even a fat porcelain pot of marmalade with a little knife to go with it. Mrs Hudson fussed with the coverlet.

“Really, Mr Watson --”

“John, please,” he begged. She smiled.

“Of course, love. Bit of a breeze coming in, shall I close the window? Perhaps put up the coverlet.”

The coverlet felt like a soft cloth prison. John wanted nothing more than to smell the sea breeze, which to him smelled faintly of ozone and Sherlock. He watched her close the window.

“Thank you for breakfast,” he said. _And for everything._ It was amazing how having trimmed nails and clean hair brightened his perspective.

Mrs Hudson hummed contentedly and poured piping-hot tea for him. John watched the leaves swish and settle in the cup, thinking of Sherlock’s plumage swirling in the waves.

“Mh-hmm?” Mrs Hudson hummed, inflecting up at the end to turn it into a question. Expectantly.

John took a bite of bread.

“Mmm-mm,” he said, and Mrs Hudson beamingly took her leave.

John chewed slowly and stared out the window, distracted by the pain in his leg.

~  ~

That afternoon, Lestrade came back. He had been working all day down at the docks, loading and unloading things mostly, and he smelled strongly of salt and fish, and just the barest touch of pungent ambergris. John eagerly took in the scent of the sea.

Lestrade paused in the doorway, but it was just for show -- he and John stood in tacit agreement that conventional procedure was for the well-bred. He came over and sat down on the edge of the bed at John’s hip.

“Made a King’s ransom down at the docks today, all things considered. How are you feeling?”

“Like shite on toast,” John said, deadpan.

Lestrade burst out laughing.

John smiled a little. The expression felt strange on his face, but Lestrade didn’t seem to notice. “You need a shave, mate. Can hardly see the man under all that bristle! I’ll bring up some hot water and a razor.”

“Thank you,” John felt as though he was missing a social cue, here, but could think of nothing else to say.

Lestrade stood up and stretched stiffly. Sherlock was all water, fluid and feline, but Lestrade was planted firmly on earth -- sensible, perfunctory motion.

“Off to bathe. Can’t stand the smell of myself,” said Lestrade, and he left for quite a while.

John spent that time wondering what Lestrade looked like naked.

Presently, Lestrade returned looking quite refreshed. He smelled blandly of soap. He bore Mr Hudson’s old shaving-tackle and a pitcher of scalding-hot water, which he poured into the porcelain washbasin on the dressing table.

John managed to get into the bald little wooden chair without falling on his face. _Point to you, Watson_.

Lestrade spoke as he organized the tools: “Used to do this for my father toward the end, but, ah. He had less hair.”

The first thing Lestrade did was prop a mirror up against the bottom edge of Mr Hudson’s portrait frame and the dressing table. John suddenly caught sight of his own, unmuddied, reflection for the first time since he had become marooned.

He looked savage.

His wild mop of too-long hair looked like it had been caught in a windstorm, and it was the lightest it had ever been, courtesy of the Mediterranean sun. His beard -- _Good heavens_ , John thought.

He looked like a man who had walked slowly through hell and then turned right back around to pick up something he’d dropped along the way. He looked like a man who had been living alone on an island for ages. He looked like a man who had killed another man.

Lestrade turned with a pair of shears and said, unapologetically: “Going to have to trim down your beard. Hold still.”

_Snip. Snip. Snip._

Clumps of tawny hair drifted to the floor. Lestrade had warm, square hands with blunt fingers. His touch on John’s face was deliberate but gentle.

“Lie back,” said Lestrade, having rolled up a towel underneath the back of John’s neck so that he wouldn’t get a crick. John leaned back, forced to open his thighs that he might brace his feet on the floor. The position made him feel exposed, until Lestrade draped a steaming cloth over his face and folded it in such a way that he left a little triangular window for John’s nose.

The damp, hot cloth felt wonderful against his skin and John’s white-knuckled grip on the arm rest relaxed and he listened to the sounds of Lestrade working the shaving brush onto the soap.

“My wife loved me with side whiskers, but now that she’s gone I’ve lost patience for them,” Lestrade said, unraveling the cloth and swirling shaving cream over John’s face. “Scarlet fever, it was. My youngest little girl and her mother.”

He stropped the razor.

“You know, I don’t know if I ever thanked you,” commented Lestrade, sliding the rough pad of his fingers under the line of John’s jaw. He pressed a little, and John haltingly exposed his throat to the blade.

If Lestrade wanted, he could cut John’s throat. His luck might finally run out, red on the floor of Mrs Hudson’s spare bedroom, and he would never see Sherlock again.

It was this thought that made John’s hands curl into fists on the armrests. Lestrade leaned in close to make sure he didn’t miss a spot as he pulled John’s skin taut and carefully scraped away.

John became more and more tense as this went on, barely able to keep still in his chair, until Lestrade wiped clean his face and prepared for the second, closer shave. He touched John’s left hand.

“You’re shaking.” His voice was difficult to read.

John squeezed his eyes shut and grit his teeth. _Damn my quivering hands._ He was all anxiety, with a distant pulse of something that threatened to transform into arousal if he wasn’t careful.

“I should have realized,” Lestrade shook his head ruefully. “I’m a bleeding idiot, Watson, I wasn’t thinking. You need time, to adjust to--”

“No!” barked John and Lestrade paused. “No, I… I don’t want to be coddled. I’m glad you treat me --” _like I’m any man, like I’m not mad or broken or_ “-- the way you do. I just. The… my time on the island, I became accustomed…”

“To survival?” Lestrade suggested mildly.

John said nothing.

They looked down at where Lestrade’s fingers still grazed his hand. John saw the moment that Lestrade noticed something. “Cor, that’s quite a scar. How did you get it?”

John looked down at the scar in the center of his palm that matched Sherlock’s. Sherlock had Sung the fear right out of him as their hands pressed together. John remembered how steady Sherlock’s pulse had felt.

“I stabbed myself in order to break free of Sherlock’s siren Song,” said John.

Lestrade’s jaw honest-to-god slackened. “What?”

“I stabbed myself in order to break free of Sherlock’s siren So--”

“I heard you!” cried Lestrade. “It sounds mad when you say it aloud, man, you must understand. If Mycroft hadn’t done the same thing to me I would have trouble believing you.”

“It has to be experienced to be believed,” John agreed dully.

“Did it work? Did you break free of it?”

“Yes.”

Lestrade let out a low whistle of amazement. John wasn’t sure what compelled him to add what he did next, but say it he did: “He has a matching one.”

“A matching what? Who?”

“Scar. Sherlock does. On his palm. I stabbed him, too.”

Lestrade’s brow furrowed beneath its sleek cap of silver hair. “Watson, just how much stabbing do you _do_ on a daily basis?”

“Only as much is as necessary,” was John’s crisp rejoinder, and then Lestrade was shaking his head and chuckling, and John was laughing with him, and the tension in the room ebbed away.

“Come on, let’s finish this. The water’s getting cold.”

Feeling light, John sat back again and let Lestrade soap and shave him in efficient, brisk silence. Then John asked if Lestrade would cut his hair, and Lestrade tried to demur but John insisted.

“There. Now you’re a right society man,” Lestrade assured him, stepping aside so that John could regard himself in the mirror.

 _My god_.

With his giant golden beard removed, there was no longer anything to distract from John’s eyes. A clean-shaven face lessened his feral appearance somewhat. Hopefully he was likely to be considered indigent anymore.

Lestrade put away the shaving-tackle, even as a little knock came at the door. Mrs Hudson peeped in.

“Yoo-hoo,” she said. “Mr Lestrade, I was hoping to catch you before you went to Angelo’s. I have a parcel I would be most grateful if you would deliver. Oh, _John!_ ”

She nearly dropped her parcel. John wished he was able to stand under his own power so he could be anywhere but here, subject to such delighted scrutiny.

“He’s got such eyes,” stage-whispered Mrs Hudson, but the appreciation in her voice wasn’t feigned in the slightest.

“That he does!” Lestrade said affably.

 John flushed. “Just… help me up, would you?”

Later, he was alone, John sat up in bed with a hand-mirror face down on his lap. He had been sitting like that for ages, trying to get the courage to look at himself again. Finally he took a fortifying breath and lifted the mirror.

It was the same man from earlier. He looked small, lean, hard. His eyes were scalding blue. His skin was brown as a nut all over, and his hair so sun-scalded that all of his natural color had gone quite cornsilk.

“I am John Watson,” he said, watching as the mirror man insultingly spoke at the same time. The stranger’s jaw was set tense, biting. His thin lips were taut with stress in a weather-lined face.

“No. You really aren’t,” the man in the mirror replied darkly.

~  ~

That night, John suddenly lost consciousness.

With an undignified jerk, his stomach dropped like someone had yanked away the bed. He swung his arms out to catch himself on the edges of the mattress, but his fingers closed on fistfuls of water as he sunk.

Spluttering, John bobbed to the surface. It was high noon, blinding brightness gleaming off the sea waves and searing his salt-crusted eyes. Something was wrong, though: there were no gulls, and although it was bright there was no sun in the sky. Obviously this was some kind of dream. He trod water until he felt the anticipated vibrations from the deep.

A bone-cold hand gripped his ankle and yanked.

John hoped it was Sherlock, and he did not resist -- although he did crane his neck to see as he was dragged below.

It wasn’t Sherlock, and it wasn’t Mycroft.

It was a giant woman’s face.

No, not a woman. It was an undine, but her head was three times larger again than a human being’s, and her body larger still in proportion. Her great hand clasped his ankle. There was something deeply unsettling about seeing a human-like body the size of a whale.

Her eyes were possessed of the cuttlefish-pupil, and so verdant green it brought to mind a land-animal, untouched gardens and Welsh grass. Her body was eel-like and her scales the green-black of wet kelp. A shredded dorsal fin followed the snakey length of her. Her torso was slit with gills. She had no breasts, but rather a bony sternum that protruded like a keel from her narrow chest.

Her hair was shorn close, and the same greeny-black as her lips and gums. Pale scars criss-crossed her scalp where oyster shells had cut too close.

She was frightful. She was magnificent.

John knew who she was.

_“Johnwatson.”_

“Undine,” dream-John said, and he could breathe water.

“ _What have you done to mine own son? Sang him to you, without a voice of your own,”_ her voice was deep, ageless. They were still sinking.

“I did no such thing.”

“ _Did you not? No voice of your own, and yet you Sang him. Mine own poor son. Perverse to desire you. Will he not lie with my daughters? I send him my fiercest daughters, the hungriest of mine own brood. He chooses his own brother.”_

Her laughter formed a lazy whirlpool. John flailed to stay somewhat upright. Through the veil of bubbles, John noticed the slow-moving silhouettes of sharks and he had to quell panic. “Undine, please. How is he? Where is he?”

Her tail came around like a bullwhip and encircled him, a motion terrifyingly fast even underwater, where everything was supposed to be liquid slow.

“ _Presumptuous little meat. Shall I tell you? No. Perhaps I shall eat you.”_ Undine did not know how to smile. Her teeth were bright needles in black gums, like bits of broken glass.

“I’d... rather you not. Just tell me what you know. Is Sherlock all right?”

Undine’s eyes narrowed. Her lip uncurled.

“Please, Undine.”

“ _Quiet, you little beggar. He tears his own fins with grief, he hungers but does not feed. He swims through blood. Mine own children have no Voice of their own -- it is Undine’s own gift. Sherlock broke his own promise. I took back his own Voice. Fair is fair._ ”

“Give it back,” John whispered.

Undine’s gills flared out. John’s instinct shrieked for him to flee. Instead, he fought his way through the current to her side.

“Give it back,” he repeated, clutching her arm so that he could not be sucked away.

She stared down at him. This close, John could see the slippery veil of nictitating membrane on her eye. “ _You tell me what to do, oh little finless one?”_

“You must give it back to him,” John begged, eloquence stolen by desperation.

“ _The agreement was orchestrated between mine own unfortunate son and you, Johnwatson. You must renegotiate with him.”_

She reached out and stroked the back of her terrible claw down the side of John’s face. Her cuttlefish eyes looked bemused. “ _Why do they always do this? What does he see in you?_ ”

“Sherlock’s voice means everything to him. He --”

“ _Silence now, Johnwatson. I will think.”_

John woke up on the floor, his face plastered to the hardwood. His leg ached and the armpits of his nightshirt were damp with sweat. He rolled over and stared up at the ceiling, listening to the sound of rain on the roof. It was dark.

 _Undine is real. Sherlock. Cor, Sherlock_!

His brain was too big for his skull, his bones swollen with seawater. He crawled to the end of the bed, where Mrs Hudson had left her late husband’s walking stick, and he used it to haul himself up. He limped to the Oriental folding screen in the corner, over which a plain pair of linen trousers were draped. With trembling hands, John drew them on. He hobbled to the door and threw it open.

He had to hurry.

He glared down the stairs. Those seventeen steps were going to be hell. The pulse pounding in his thigh warned him not to try it. John went anyway. _Sherlock. I have to get to him. I cannot wait a moment longer_.

Somehow he reached the landing with the front door and the door leading to Mrs Hudson’s rooms. His clumsy fingers rattled the handle when he tried to open it.

“Who’s there?” Mrs Hudson’s voice was faint with fear on the other side of her door. “Mr Lestrade? Is that you?”

If he could only get to the sea, everything would work out.

John finally managed to unlock the door and he skidded out onto the slippery stoop. The wind pushed a gush of rain against his back, and it was as though the sea herself were nudging him along, saying, _go to him John Watson._

A young couple, unbothered by the rain, walked up the street. They stared open-mouthed as John stumped frantically past. Presently, a familiar head came up the cobbled street. He flung himself into a nook between a butcher shop and a residential. Lestrade was trying to turn his inside-out umbrella outside-in. He did not see John. John waited until splashing footsteps faded and went back out onto the thoroughfare -- but then his leg suddenly gave out, cane or no, and he went down with a grunt.

He could not get up.

His brain was pea soup.

He was useless.

Sherlock was waiting for him in the ocean, Sherlock _was_ the ocean, and John could not go to him. John put his face in his hands and experienced a wave of self-loathing so raw that he wished lightning would strike him dead. His thigh pulsed hotly and pinkish blood stained the cobblestones.

“Watson?” Lestrade’s voice came to John like a bubble drifting to the surface. “Sweet Mary!”

“Oh, oh --!”

“Cor, Mrs Hudson, he’s burning up!”

~  ~

When John’s veins had decided to pump ice water instead of blood he didn’t know, but he simply could not get warm. He trembled and groaned, slick with sweat. Papery small hands fluttered over him, pressing cool wet cloths to his brow, so wet, water, ocean --

“ _Sherlock_.”

“What was that?” Mrs Hudson’s voice floated down.

Lestrade’s remark came soft as an echo. “Nothing. He’s speaking nonsense. You know how fevers addle the brain.”

John grit his teeth. _I want Sherlock._ Whiteness encroached on the edges of his vision until he was lost in it.

~  ~

The next evening, Lestrade came in and sat across from John’s bed and looked at him.

“I’m not stupid. I know that you’re going to try again, to do whatever it is you think you’re going to do. Get back to that island, I suppose? Don’t you deny it.”

John could not deny it. So he didn’t speak. Lestrade sighed so heavily that his entire body sagged into the wooden chair, which also sighed. “You can’t row there on your own. Let me take you.”

John’s head snapped up so fast he felt something twinge in his neck.

“Hah! You’re like Ahab with his whale. I haven’t forgotten what you told me on the clipper. You’re not giving up on seeing your mermaid, are you?”

“Man,” John corrected faintly.

“Man.”

“I can’t rest until I see him. He’s hurt. He needs me,” John admitted, and was horrified to hear that his voice had broken.

“I can’t just let you row off to your death. You took a bullet through your thigh. I stuck around here, didn’t I? You’re not the only one invested in your own survival now, Watson. That’s why I’ve rented Angelo’s old sloop.”

 John knew that Lestrade’s savings had been going toward procuring them passage back to London. A wisp of excitement ate up the guilt. _A ship. He’s got a ship. I can get to the island now._

The guilt must have shown on his face because Lestrade held up a callused hand.

“No false protests, Watson. We both know you’d search for ‘im if it wore your leg down to a stump. Think you made that right clear yesterday.”

“When can we go?” John asked.

“When you can walk without limping.”

John let out a sharp grunt of displeasure. “That’ll be months, if not the rest of my bloody life.”

Lestrade reconsidered. “When you’re able to swim. With your luck you’ll end up in the water again. A cat only has so many lives.”

“Deal,” John said so quickly he accidentally cut Lestrade off. “I can do that right now.”

“No, you absolutely cannot, and if I catch you going down to the sea and jumping in like a madman I will sit on the docks and watch you drown, John Watson, mark my words. When your wound scabs up enough to keep the salt out, and not a moment, not a bloody second, sooner.”

John was still getting the better end of the bargain. He studied Lestrade, who fidgeted self-consciously, rubbing his broad hand over the back of his cropped silver head.

“All right,” he agreed.

 

His wound scabbed up, and the time passed rather less torturously than expected. Knowing that he would soon play an active role in finding Sherlock calmed him. He stayed off of his leg. It was a struggle to relax, and John had to consciously remind himself that he did not need to forage. Lestrade brought him fishing nets to mend, and other small tasks that could be done bedridden.

A week later, John was sorting through a giant bowl of cannellini beans. He picked out the bad ones and threw them in a burlap sack on the floor, glancing up briefly when Lestrade came in. His breath smelled of grappa _,_ which meant he’d been having a nightcap with Mrs Hudson.

“Why do you love him?” Lestrade asked without preamble.

John blinked. “Hello to you, too.”

“On the _Appledore_. You said you’re in love with the mer-- the undine. I’m curious how that happened,” Lestrade sat down on the edge of the bed, and the bowl tilted with a rattle.

John tossed a bad bean at Lestrade. It bounced off of his leg and fell back into the sack on the floor. “You wouldn’t believe it.”

“Wouldn’t I?” insisted Lestrade. “I’ve already _seen_ the undine, Watson. Spoke with ‘em too, didn’t I? Been on Magnussen’s fool errand for ages, and I’ll admit the evidence was compelling even before we caught that first one.”

John’s heart grew heavy with the memory of the poor, dead undine that Magnussen had captured and rigged up to his sonic machine.

Lestrade leaned in close. His breath was brandy-sweet. “I want to understand. Go on, then?”

So haltingly, in fits and starts, John did. He started at the beginning, with the storm on the _HMS Endymion_ and how he and Sherlock had stolen breath from each other. How Sherlock had taken him to land only to trap him. He confessed to Lestrade how afraid he had been, how alive he had felt, how his time marooned had shrunk his world to survival.

Over cannellini beans and a bullet wound, John confessed how lonely he had become -- hell, he even mentioned naming Wylie Clegg, but Lestrade didn’t so much as smirk. Thus encouraged John plowed forward despite the heat rushing up the back of his neck and the tingle in his palms. He told the tale of the Named Ones out of order, starting with Lahosiel.

Lestrade seemed more put off by John’s experience with the bends than the inconceivable concept of diving hundreds of feet below to interact with a betentacled leviathan.

The sun had long set and the room was lit by flickering lamplight. Somewhere along the line the distance between them had lessened.

John touched Olizarat’s tooth where it lay heavy against his chest, now on a metal chain Mrs Hudson had supplied. The tooth held dual significance for him: like the bullet he used to wear around his neck, it was a symbol of what he had overcome. A lucky talisman. Its second meaning was Sherlock… a physical reminder that the undine was real, his experiences on the island had been real, and that he was not barking mad.

_Perhaps some stories are best left untold._

“What’s that, then?”

Lestrade looked so warm and rumpled and inviting where he sat across from John. His legs were tucked underneath each other and his arms were folded over his broad chest.

“The tooth of another leviathan,” John said, studying Lestrade for any signs of mockery. “The undine called her the Destroyer, and she was slain by Sherlock and Mycroft.”

John ducked out from beneath the chain and held out the tooth, root-first. Lestrade took it. He looked it over. Then it belatedly dawned on him and he nearly dropped the tooth in surprise.

“Wait. This is a leviathan’s tooth?”

John nodded curtly.

“Sweet Mary.”

John nodded again. He stirred his fingers through the cannellinis. Lestrade’s warm tenor drifted through the muggy air.

“You’re leaving things out. Things like how you fell in love with him,” and John thought he must be imagining the rueful note to Lestrade’s voice.

 _I’m not bloody well telling him about the Riptide_ , John thought. He scrubbed a hand over his face to disguise the flush. _Cor._

“You’re blushing!” crowed Lestrade, an irritatingly observant drunk, and he leaned forward to playfully shove at John’s shoulder. John fell back in order to prevent his leg from being jostled and glowered up at the bigger man when some of the beans spilled onto the sheets.

“And you've had too much to drink, my friend,” John choked out at last, tone less a growl than he would have preferred.

“Then you aren’t in love with him?” pressed Lestrade, leaning over John and crowding him against the pillow. Like John, he also had a small tattoo on his inner bicep -- but unlike John, it wasn’t a faded old anchor. It looked like…

“A fox,” Lestrade said, noticing John’s gaze and using it as an excuse to flex.

John snorted. “Get off. Help me with the beans.”

Lestrade sat back. “I spoke to Mrs Hudson tonight. Told Angelo we’ll be gone for upwards of a week to be safe, paid up front. He’ll refund us the cost if we come back earlier, so really the sooner we get there and back again, the better. Mrs Hudson is worried.”

“When isn’t she worried?”

“True. But she isn’t the only one.”

“Angelo’s no shrinking violet. He barely knows me. It’s your labor he’ll miss. What was that he said? You’re ‘the most competent man he’s employed in years’?”

“Not Angelo,” said Lestrade. “Me.”

“You.”

“Me.”

“ _You’re_ worried. About what? The only leviathan that would pose danger to us is dead, and Sherlock would never hurt me. Or you, if you’re with me,” John added hastily, and hoped he was right.

“I won’t lie, John --” oh, there was his Christian name now, “-- I’d have poor survival skills not to worry about being in the presence of man-eating merfolk. Does Sherlock return your feelings?”

He remembered how Sherlock had saved him from death by keelhauling, and then --

_John cursed. “Sherlock, please! I’m begging you, for the love of god you must flee. He has a machine.”_

_“A what? I will not go, John. You can barely swim.”_

\-- he had refused to abandon John. And it had cost him everything. John swallowed hard beneath Lestrade’s too-intense stare.

“That’s what I intend to find out.”

~  ~

The _Honeybee_ was an appealing little sloop. Even moored next to the impressive _Al Dente_ , Angelo’s new ship -- and certainly the reason he had been willing to part with the _Honeybee_ to begin with -- it looked cheerful with its yolk-yellow sail and peeling buttermilk paint. It was a single-masted lateen in the Bermuda style, and though popular in the Mediterranean, a make rarely seen in English waters.

“She’s an old girl, but she can really fly. Got a steering oar instead of a stern-mounted rudder, see, and to be honest I’ve only taken her out twice -- and that was when the _Al Dente_ was in use,” Lestrade said apologetically as he loaded their victuals and water tuns.

John was not paying attention. He was so blindingly happy and eager that the pain in his thigh was entirely forgotten,  and he stumped briskly across the deck that he might touch the furled yellow sail.

“I gave the deck a good swab a few days ago, although I’m sure it’s not the first deck you’ve kipped down on. We’re going to smell like fish for days.”

John turned his clean-shaven face into the wind. _God. Yes._ He was grinning so hard the wind chilled his teeth. He turned to look up at Lestrade, who was maintaining the anchor rode, but paused when John caught his eye and beamed up at him.

“She’s perfect,” he breathed.

Lestrade stared at him. The bight in his hand loosened, but he didn’t seem to notice.

John said, “Come on, let’s get her going.”

The sun had risen far above the boom hours later, which saw the _Honeybee_ sailing merrily along with its sunshine sails unfurled. Lestrade was somewhat confident he could get them back to Sherlock’s island, or at least in that vicinity. They set a course southeast.

The wind was mightily in their favor. 

~  ~

John saw it first.

The island manifested as a lilac smudge on the pale blue horizon, and John cried out and stood so quickly that his leg spasmed and he stumbled against the stern.

“Careful!” Lestrade bellowed. “What is it, man?!”

“Land ahoy,” John croaked. “There it is.”

“How do you know it’s the right one?” asked Lestrade with a smile.

“I’d know that island anywhere,” replied John, and he was right.

There shone the sugar-white sand. There sprang the hodgepodge of a forest hardy little fan palms, and there grew sparse scrub, like day-old whiskers on a man’s cheek. And there. There was the rocky outcropping of Sherlock’s lagoon. Lestrade found a current and began to guide the _Honeybee_ around the shore. Any minute now, Sherlock would come out to investigate the intruders.

John scoured the water for a sleek black head… but it didn’t come.

They made a full circuit of the island, and Lestrade made a second circuit without being asked. John looked for a fin, a splash, a dark shape in the water -- anything at all. But the waters were placid. Even the waves seemed less rebellious than usual.

“Let’s land,” John said. Recalling those deadly guardian currents that protected the lagoon on the other side, John had them go to instead to the beach where he had camped. Sure enough, the ugly tree still sat there like a squat black spider.

Beaching the sloop was a complicated little maneuver, but the tide was favorable and would continue to be so until the evening. The _Honeybee_ was no dinghy -- it would require more than just two men to turn it around to face the ocean when they grounded her. She’d come in bow-first.

“We’ll run her aground and trust that the evening tide won’t drag her out,” John said.

“All right.”

The _Honeybee_ slid smoothly up onto the sand. Once she was anchored, John swung his travel pack over his shoulder and yelped when the rough strap put pressure against the shiny red scar where his nipple had been.

Lestrade blanched. “Argh.”

“Don’t say it,” gritted John.

Lestrade said it. “I’m so sorry, John, I --”

“I said don’t bring it up,” John said briskly. “You spoke up when it was decided I was to be keelhauled, and that’s good enough for me. Lestrade. If you’d protested any more than that, Magnussen would have tossed you over with me, and we’d both have to live the rest of our lives without that oh-so-important bit.”

Joking didn’t change Lestrade’s guilty look.

“Come on then. I’m going to look for Sherlock. You’d better come in case my leg acts up, yeah?”

Lestrade tightened his bootlaces, “Let’s be back before nightfall?”

John grunted. He took up the late Mr Hudson’s walking stick. An item of such exquisite craftsmanship was incongruous on this island, but it would have to do. He let Lestrade help him off the sloop because he wasn’t sure how his leg would take to being jarred if he jumped.

There was an awkward stumbling in which John overshot and for a brief moment he was pressed again Lestrade’s firm, sun-kissed body, and he hurried to put polite distance back between them.

There was already sand in John’s boots, and it reminded him of when he’d discovered the human phalanges on the beach. It reminded him of how Sherlock had barreled up onto the beach after him.

Lestrade’s hand was warm on his shoulder. “All right?”

John grunted a non-answer and began to lurch along the beach, listening carefully.

“Where are the crabs?”

“What?” said Lestrade. He was investigating the obviously man-made structure of driftwood and plank that John had stacked up against the base of the ugly tree ages ago. “What is this? Did you make this?”

“A shelter,” John replied shortly.

“You _slept_ in this?”

John frowned. “I can’t hear the birds.”

“Christ. This makes me miss my bunk in the frigate. Ah, look here. I can see where you made a fire.”

“Can you hear the birds?”

“What?” Lestrade was poking at something dead with a piece of driftwood.

“Can you hear the birds?” John repeated. “Listen.”

They listened.

The island was unusually quiet. There were no gull cries, no blowing of distant whales. The only sounds were the soft wet slap of the waves and the lonely whistle of wind.

“Better search the island,” John said at last. He made his halting away around the perimeter.

“What, in case he grew _legs_ and is just -- just catching some shuteye somewhere?” Lestrade drifted after John anyway. “It’s so quiet here. Was it always this quiet? S’pose you sang a lot to keep yourself occupied. _Oh, Nancy Dawson hey --_ ”

“Shh,” said John.

Lestrade chuckled, unoffended.

John saw evidence of himself here and there: a pile of half-sharpened javelins sheltered by a palm frond, a bird-picked pile of crab carcasses in the fire pit, strips of bark he had gathered to weave rope. There was no sign of Sherlock.

Lestrade became quieter and quieter as he followed.

“I can’t believe it,” he said finally.

Distracted, John spoke over his shoulder. “Pardon?”

“I… you really did survive on this island all alone. For months.”

John felt a muscle in his own jaw jump. He focused on navigating the difficult terrain.

“I -- it’s not that I didn’t believe you, John. I wouldn’t have gotten us the _Honeybee_ if’n I didn’t. It’s just… the hardest part of the story to believe wasn’t the bits about Sherlock and Mycroft.”

John stopped.  “I don’t care if you believe me or not.”

It wasn’t true, but he was feeling prickly and there was something hot and sad swelling in his chest. Lestrade, easygoing as ever, just said, “Well anyway, I _do_ believe you,” he uncapped his canteen and gulped drinking water. “Say, what did you drink _?_ ”

John found himself drinking from his own canteen carefully. “Come on. I’ll show you.”

It took them the better part of the day to scour the walkable part of the island. John pointed out his rainwater collection system to stave off the unearthly silence. The big flat leaves, coconut halves, and dished rocks were overflowing with stagnant water.

“I have a theory that this island sees more rain than most. It’s the Mediterranean. It hardly ever rains.”

Lestrade agreed. “That is peculiar. And the storm that caught you up on the frigate to begin with…”

“Curious, isn’t it? I think it’s related somehow to the fact this place is Sherlock’s territory. He loves storms.”

John stared out over the waves until the back of his neck prickled and he became aware that Lestrade was no longer watching the sea. He cleared his throat and began to pick his way down the beach, taking care to pick his way carefully so he didn’t land on his arse.

It was late afternoon, now, and the sun drifting lower.

“Don’t know about you, but I’m hungry,” Lestrade said, with an expression too close to pity for John’s liking.

They returned to the _Honeybee_ and unpacked a dinner of salted ham and pickled gherkins. John spread marmalade on top of the ham, and then he did himself one better and put a gherkin on that and ate it all with relish. Crabs had been so much effort to break into, and half the time they were flavorless and rotted on the inside.

 _Mmm_ , _real food. Thank god for real food._ _In particular, thank god for marmalade._

There came a splash in the sea, and John sprang to the stern with such alacrity that he knocked over the open pickle jar. It clattered across the deck expelling gherkins.

“Sherlock?”

But there in the shallows glided two curious dolphins. Lestrade came up beside him, wiping pickle juice off his trousers. “Cor, would you look at that! I love dolphins. Hullo, there.”

The larger of the two rolled onto its side to stare up at them from the waves. John saw the scar on its melon and recognized it as one of the pair he’d met before.

“Stamford. What are you doing so close to the island?” John muttered apprehensively. Their curiosity about the sloop shouldn’t have been so strong as to override their natural fear of the undine.

Lestrade unlaced his boots. “Stamford? Awwwr, Johnny. You _named_ him!”

“Come off it,” John snapped, fear for Sherlock eliminating what passed for his patience. “They shouldn’t be this close to the island. They’re cautious of Sherlock, and -- what are you doing?”

Lestrade grinned his bright white grin. He had taken off his boots and socks, and there went his shirt. He sat on the bulwark, kicking his legs over the side deliberately. “S’not every day a man gets to see dolphins this close.”

He made kissy noises at them, which had them sticking their snouts of of the water to squeak back.

“Feels good to be loved,” Lestrade said. His grin turned a little mischievous. “Don’t get jealous, mate, you’ve already got your own!”

The corner of John’s mouth twitched. “Careful what you wish for.”

Then he slipped off the edge of the sloop and into the water, and immediately the dolphins swarmed upon him with the exuberance of dogs. Lestrade laughed out loud at their boldness, just as delighted as John had been when he first met them, and John found that he couldn’t remember what he had been saying.

The sight of Lestrade and the dolphins gallivanting stole his breath.

“What are the chances that someone like you was working with Magnussen?” John mused aloud.

“Come again?”

John shook his head and waved Lestrade off. After a time Lestrade climbed back aboard the _Honeybee_ dripping wet and panting. “I’m going to sleep like a stone. Such friendly wee babies, aren’t you? Aren’t you? Yes you are. Yes you are!”

_This is a grown man._

John snorted. “If you’re done coddling the dolphins --”

“Which is no stranger than talking to mermaids.”

John’s cheek twitched. “There’s one place left Sherlock could be.”

“The big rock?”

“Yes. It’s actually a lagoon.”

“S’it really?”

“Yes. You can only get to it by water. And last I saw, Sherlock has constructed these, these sort of rip tides at all but the narrowest entry point. I nearly drowned trying to escape.”

“How are we to get inside?”

“Not ‘we’. I’m going alone.” John held up his scarred palm to forestall Lestrade’s argument. “That space is not for humans to enter. It’s the heart of Sherlock’s territory, and honestly it’s the likeliest place for him to be. If you enter there, I don’t know what he would do.”

Lestrade looked down at John from his scant advantage of several inches. John stared evenly at him. Lestrade looked away first, scrubbing his hand through his wet silver hair and turning his back to John to dry himself.

“Lestrade…”

Lestrade procured dry clothing for himself from the luggage trunk. “As you like, Watson.”

 _Oh, so we’re back to Watson, now?_ John frowned. He stepped forward to explain himself, but in his distraction forgot to make use of the cane and hit the deck, hard. Lestrade appeared at John’s side fast as a whip snap.

“Tarnation, John!”

John grit his molars so hard they probably made powder. His thigh was pulsing hot with pain. “Nngh. Forgot cane.”

Lestrade nudged the cane into John’s clenched fist. “This is exactly why you need someone to come with you. What if your leg gives out and you drown, or hit your head on a rock?”

“I’ll be fine, Mrs Hudson. Thank you for your concern. I need you to bring me to the shoal there.”

“It’s almost sundown.”

“Then we’ll go quick,” John said, hauling himself carefully to his feet with the use of the cane. “I know the grotto as well as I need to, and believe me it won’t be the first time I’ve stayed there overnight. Just… why don’t you collect me in the morning, yeah?”

Lestrade was not happy about being delegated ferryman, but he did stow anchor and pull them back out to sea as the sunset turned the ocean to rust. They gave the mouth of the lagoon wide berth for fear of the guardian currents, but it turned out to be unnecessary.

The waters were calm upon the twin shoals.

Too calm.

The cave entrance yawned open enormous before them, and although they were not close enough to see clearly inside of it, Lestrade let out a low whistle of amazement. The gravel shoals bracketed the shallow water leading up to the unscalable cliff face, and in the sunset the black rocks shone like blood, studded with algae and limpets and salt deposits.

The hairs on the back of his neck stood on end.

Something was very wrong.

“I’m going in,” John heard himself say, lowering himself carefully into the shallow water by the shoal, as close to the _Honeybee_ as he could get. Lestrade passed down his overnight pack with the lantern in it, and his boots and cane on top of that.

Lestrade looked uneasy. “I’ll be back tomorrow to collect you, John.”

“All right. Don’t come in, though. Just… I’ll come out here.”

 Lestrade snorted.

 “I’m serious. Don’t.”

 “So many rules to follow,” teased Lestrade.

 “You have no idea,” said John, and with confidence he did not feel he added, “I’ll see you tomorrow.”

**Notes for the Chapter:**

> Anyways, we're in the home stretch now! Please don't ask me how many more chapters I have to go because I won't know until we're done, I suck at guessing (my current penciled in guess is at least two more to wrap up the main storyline plot, perhaps??)
> 
> There is an undine!Sherlock Riptide Lover cosplay now. AND AN UNDINE!MYCROFT. ~heavy breathing~ These can be enjoyed on the blog. Check it out! Also, a reader made an awesome [fan-composition](http://jinglebellfic.tumblr.com/post/139701676776/jinglebellfic-aufanficfanatic-inspired) inspired by RL (and now on the [inspiration playlist](http://8tracks.com/jinglebell-fic/riptide-lover) I like to listen to while I write). 
> 
> I'm always humbled and delighted beyond words by the creativity of this fandom. You all have added sparkle to my life.


	19. Mine Own

**Notes for the Chapter:**

> It's 221b Con 2016 eve!! Red and I have worked our arses off to get this chapter up. Fun fact, I teared up writing this chapter! /nerd alert 
> 
> Brace yourself, emotions are coming (and it's about damn time if you ask me)

John knew Sherlock was not inside the grotto.

He couldn’t say how he had known. He thought it unfair that his precognition did nothing to guard against the way his heart sank.

“Sherlock?” _Sherlock, sherlock, erlock, lock, ock, ck...._ His voice bounced through the chamber.

He waded to the flat rock and put down his pack, grateful at least for how the water made him buoyant. It took the strain off his leg. He rummaged about inside his bag for the little kerosene lamp.

He unraveled the rags that had been used to cushion the glass and spent some time hunched over the damn thing until at last it lit, and then he nearly knocked it into the water on accident. Cheerful light tinted everything in tones of sepia, illuminating well the first ziggurat step. It was conspicuously barren of Algernon Portnay Kirk’s treasures.

Concerned, John waded closer and cursed when he stepped on something sharp.

Gold sparkled between his toes, and he lifted his bare foot. Out of the sand poked the tines of a fork, and nearby he saw half-buried the rest of the golden cutlery set. Closer to the back wall was the empty violin case, filled with sand.

“What God’s name..? Sherlock! Sherlock, come out.”

John circled the flat rock, dragging his toes to kick up clouds of snowy sand. On the other side, he found a piece of the pegbox from the violin… but no sign of the rest of the instrument.

“The cutlery didn’t spill itself,” John told the air, accusatory. He climbed up onto the rock and looked out at the sea through the grotto entrance. He couldn’t see the _Honeybee’_ s sail, which meant that Lestrade had gone. John was quite alone.  “I know you’ve been in here. Did… did you abandon your territory?”

His shoulders hunched in. He drew his knees up to his chest. He stared at the water, so clear that it may as well have been air.

The grotto seemed so large without Sherlock in it.

Empty.

John squeezed his arms tightly around his legs, until his thigh twinged warningly and the compression made breathing difficult. Olizarat’s tooth stabbed uncomfortably into the flesh of his lower belly.

“Sherlock?”

Even though John well knew Sherlock wasn’t going to magically manifest on a cloud, he turned his gaze skyward, looking up through the hole in the cave ceiling. The sky was the color of an orange rind, filled with purple sunset clouds.

He sat alone for a very long time.

~  ~

He lurched awake.

John's fingers were still laced over his shins and his body was locked up tight, fossilized there on the flat rock like a gargoyle. The night sky was black velvet, but the little kerosene lamp was still lit. The waves lapped quietly at the rock.

Then he spotted it. It was pure happenstance; the current peeled back the sand blanket just enough to catch a glimpse.

 _Oh no_. _No, please_.

He leaned over to dip his arm in the water, scooping up the familiar thing. He held the fistful of sand for a long moment until he felt able to uncurl his fingers in the light.

It was his lucky bullet.

The sight of it filled John with unfathomable grief. The acid tang of fear poisoned his mouth and bile rose.

Why was this here? What had happened to Sherlock?

Sherlock was the only one who knew him. He was the only one who had seen all of John, stripped bare of the comfort of civilization. John wounded and been wounded, and he had survived -- and the entire time he had thought himself so terribly alone, because he had thought Sherlock irrevocably inhuman.

And yet...

For some reason, the memory of the time he and Sherlock had play-acted at a marriage proposal rose to the surface. John recalled being amused at first. He recalled the way his mouth had slowly gone dry as Sherlock looked at him with those stunning silver eyes, and how John had suddenly hoped he passed muster, laughing nervously when Sherlock had whispered _yes_.

His hand shook.

The bullet rolled on his scarred palm, warmed by the contact with his skin already. He had given this to Sherlock in exchange for the ability to come and go as freely as he pleased, but it had been clear that Sherlock just wanted to own something that had been important to John. In hindsight, it was obvious that it had been a childish insistence for intimacy John had not been willing, at the time, to give.

What would have happened, truly, if Sherlock had not brought him back to the island? What if he had listened to John and ferried him to land and then… left? John lingered painfully on the thought. The person he had been before would have striven to get back to his mediocre London life. Over the years he would have tried to convince himself that the undine had been a figment of his imagination after all. The niggling suspicion that he had made the wrong choice would have eaten away at that John for the rest of his dull little life.

Now, John wasn’t so far gone as to believe that what Sherlock had done was good. It had been wrong to hoard him on an island like living treasure. John’s life was far from dull now, but it would have been nice to have been offered a choice. _A choice you would not have taken, Watson. Dammit._ _Why does he have to make everything so difficult?_

As he thought about it, John became more and more distressed by the notion that he might have walked away from the adventure of Sherlock. His imagined alternative future would have been as inert and passionless as his mind had been, waiting for adventure to find him until the day he died.

John spoke haltingly, neck ramrod-straight and jaw set. “You… you went about things wrongly, Sherlock. But you tried to take care of me, in your own way. You were terrible sometimes. And I… I was terrible to you, too.”

The bullet was heavy in his palm.

Inert.

Then, softly: “I was so alone, and I owe you so much.”

He lowered his head and crouched there on the rock, pressing the bullet to his mouth with one hand and covering his eyes with the other. There was a heavy hot tightness behind his eyelids and a miserable pressure between his brows. It felt as though his heart had liquefied in his chest and been carried away in the current of his veins, a deadly rush that no tourniquet could prevent.

In his misery, John could only think the worst. Was Sherlock in the open ocean? Perhaps he had done something drastic? Why was the grotto in such a disarray? What if…

What if Sherlock were _dead_?

He might have sustained too much sonic damage on the _Appledore_. Perhaps he was already dying when Lestrade saw him. John had no idea what the long-term effects of the phonautograph might be -- after all, the only other undine on which it had been used was dead.

“No, please… Sherlock. Don’t… don’t go. Don’t be --” his voice cracked like rusted metal, “... dead. Would you do that, just for me? Just. Stop it.”

Finally, with a near-impossible effort, John sniffed and straightened his spine one vertebrae at a time, coming to brittle attention. He straightened his shirt, dusted off his trousers. He stared up through the hole in the grotto roof.

John moved to leave. Then he stopped, remembering that Lestrade was gone. Olizarat’s tooth felt like an anvil around his neck. He could not leave, but did not want to stay. Where could he go? Lestrade would not return until morning, and there was nowhere to go in the bloody grotto except --

The secret lake.

Slowly, John dropped the bullet into his trouser pocket and got to his feet. He began to climb, haltingly at first as he tried to spare his leg. When he got to the highest level, the muscles in his arms were on fire and sweat was dripping into his eyes. He flung himself onto his back and panted, squinting into the slender chasm at the base of the rock formation.

_That’s the entrance. Bit of a tight fit, as I recall._

John shimmied forward, feeling blindly with his hands, the looming press of ancient stone sandwiching him front and back; if the grotto chose that moment to cave in, he would be crushed. Sheer stubbornness animated John through the darkness and rising panic -- he wanted to see the lake one more time, dammit.

When he slipped carefully off the little ledge, into the chamber, it was exactly as he had recalled. The natural stone bridge led out into the middle of glass-still water. Moonlight threaded through the holes in the chamber roof, spotting the gravel shoal and water with discs of white.

John squinted through the dimness. One such spool of moonlight illuminated a very large form on the end of the stone bridge, serpentine body hanging half-off the edge and disappearing into the water.

_Sherlock._

John was running, his bare feet slapping stone. Distantly, he was aware of pain in his thigh. The undine was still as death, fetal on the unforgiving stone with his arms curled in. His great tail hung off the edge and disappeared into the depths of the lake.

_Sherlock oh sweet Mary it IS him, he’s not moving, he is dead, he is dead_

John fell to his knees, skin tearing as he slid towards Sherlock. He took Sherlock’s bloodless, cold body in his arms, turning him so that his face was illuminated.

“No.”

John frantically swept Sherlock’s dry curls aside to reveal cheekbones sharp enough to slice and closed eyes sunk deep in shadowed sockets. His gills were cracked and bleeding, his once plush lips parched. His rib gills were in no better condition, and what John could see of his pelvic fins were splayed out like a woman’s discarded petticoat all over the stone bridge, split and curling at the edges.

Someone was making a raw sound of grief -- distantly, John was aware that it was him, but he was numb. His eyes were hot, he was unable to breathe, unable to speak, the world around him was a blur of black and white scales and deathly, muted gray.

_What have you done?_

Then Sherlock stirred.

His eyelids shivered, drawing open slowly to unveil that familiar silver-green. His clear nictitating membrane slid across his eyes and his pupils sluggishly contracted with recognition. John felt Sherlock’s body heave, then the weight of his arms around John’s shoulders.

“Sherlock,” John choked, and then he was furiously peppering kisses across Sherlock’s forehead, his cheeks, his jaw and nose and lips. “How did you get in here? Oh, Christ, I thought I’d lost you.”

He unwound one of Sherlock’s hands from his neck and enfolded it in his, pressing it firmly against his own chest. Sherlock looked thunderstruck.

“Sherlock. Say something, please, I can’t --”

Sherlock’s soft expression hardened into that familiar, stoic mask. He shook his head, ever so slightly, and John leaned down to kiss him. Sherlock’s lips were dry and inhumanly cool. He went very still. John pressed firmly with his mouth, attempting to communicate the depth of his affection, but Sherlock remained motionless. Discouraged by Sherlock’s stillness, John drew back and what he saw drove a spike into his heart.

Sherlock was weeping. Transparent pearls of liquid coalesced on Sherlock’s eyelashes, blooming huge and quivering before tracing wet stripes down his cheeks.

_I… thought the undine could not cry._

Although John’s heart ached for Sherlock, a small thread of relief curled through him. Such a magnificent creature weeping -- something final clicked into place, a lingering doubt left unassuaged until just this moment.

A dry sob spurred John to speak. “Oh, no, no. None of that, you’ve lost quite enough water already. Your voice is gone, isn’t it? Oh, Sherlock.”

John cupped the side of Sherlock’s face, watching the undine shudder with the unpleasant novelty of tears. When his sobs abated, Sherlock dragged his tail wearily out of the water and draped in a half-hearted coil around them.

“You killed Fletcher to protect me, and Undine took back your voice,” John whispered, resting his chin on damp curls and letting Sherlock press his cold nose against the skin of his throat. “It’s all my fault. If only I hadn’t forced you to make that damned promise, this wouldn’t have happened. Sherlock, listen to me, I am sorry. I’m sorry for every way I’ve wronged you, god, I can’t count the ways I’ve been unfair --”

Teeth closed around his throat, startling him to immediate silence.

Sherlock waited John stilled, and then let him go with a brief kiss to his Adam’s apple. John returned his kiss him on the aural fin, the closest bit he could reach. Even that felt dry. 

“Blimey, you’re parched. You look half dead. Have you been doing this to yourself? Damnit, Sherlock. You’ve got to get back in the water.”

John tried to roll Sherlock toward the edge of the stone bridge, but Sherlock refused to cooperate; he was too busy sniffing the air. He sat up a bit to investigate John’s bandaged thigh. It was showing freckles of red all the way through his damp trouser leg. John wished he had somehow managed to bring the walking stick with him.

“Don’t you start fretting over me, too. It’s healing up. Must’ve torn the stitching a bit when I climbed up here.”

Sherlock canted his head to the side and raised his eyebrow.

“I should be asking you the same question. I had to climb up all those ledges in your cave, then squeeze through a crack. You didn’t climb in here somehow, did you?”

Sherlock rolled his eyes, and John was so grateful for the familiar expression of disdain that his grateful bark of laughter came out more like a sob. Sherlock kissed his neck and then shifted away, pulling himself over to the edge of the stone. He hesitated, leaning out over the glass-still water.

“Go on. I’m not going anywhere, love.”

_Love. Cat’s outta the bag, Watson._

Sherlock inhaled sharply and turned his face away. For a moment he held himself there, shoulders trembling slightly, and John wished to Undine herself that he could see his face. Then Sherlock let go and spilled into the lake in one serpentine motion.

The impact sent up a colossal splash of blue light. Sherlock swam slowly below, his illuminated figure an easy one to track. His movements started stiff but grew fluid the longer Sherlock was in his element. As John watched him drift slowly around the lake, one unconflicted emotion rose up above all the others. Gratitude.

_I am so grateful you are not dead or gone._

Sherlock returned to the rock, sleek head emerging from the water to stare at John.

“Yes?”

Sherlock dove back below and continued his slow laps. John leaned back on his hands and observed with a heart full to bursting with affection, a feeling stoked brighter every time the undine returned to make physical contact with him, kissing his wrist or bare ankle.

Predictably, he lingered on the ankle. John smiled.

The hour was late, the moon was high in the sky, and John felt absolutely no inclination to rest. Sherlock completed another circuit below and then abruptly breached, bracing his arms over John’s legs and walking himself up until their noses were touching. Water dripped from his sopping wet curls; John laughed aloud and Sherlock grinned and huffed a silent laugh himself.

That soundless laugh was a sobering reminder. He had given up his voice to protect John. That beautiful, sinfully deep baritone voice, and its supernatural ability to compel emotion in living creatures. What a treasure to lose.

Sherlock had been maddened by the sound of Magnussen’s machine, yet he had still managed to subdue -- _no, Watson, no sugar-coating it, call it like it is: he killed Fletcher_. Fletcher, who had been a threat to John’s life.

Just how aware of himself had Sherlock been during the events on the _Appledore_ ? Had he known that John was in danger at the time, or had it been an animal reflex? The events of that fateful night were mostly a blur to John, but he would not, _could_ not, ever forget the way the sea had gone still when Sherlock realized the consequence of his transgression.

“Listen to me,” John began, but Sherlock was leaning in for a kiss. John pulled back. “No, wait. I have something to say. Your voice, Sherlock. And what happened with Fletcher. I… I can’t make it right, what’s happened to you. Your Song is gone. Undine took it back.”

Sherlock’s shoulders stiffened.

John drew himself up and said, “I wish to break the terms of our agreement, and liberate you from our understanding. I don’t want to hurt you again. Consider yourself free.”

When John said these words, the air seemed to tighten around them both for a moment, like lungs contracting, and then it… let go. Sherlock’s fins prickled up along his sinuous tail and it seemed that he could not bring himself to look at John, again; he turned his face to the side and let a curtain of dark curls tumble in front of his eyes.

“Such drama,” clucked John, gripping Sherlock’s chin and turning his face. “We’re starting from a clean slate, you and me. That’s all there is to it.”

Sherlock’s hand slid along John’s wrist and alighted upon his own throat; he sighed.

“Of course it will be difficult without your voice, Sherlock, but it’s not insurmountable. There was a deaf fellow on my old frigate assignment and he got along well enough. We shall learn sign-language. You learn so fast, you’ll be teaching me in no time.”

Sherlock snorted. He flicked John’s bicep, but he was smiling a little, almost bashful, and it was such a novel expression upon his face that John leaned in to kiss it, and once their lips were touching it was all over. John couldn’t restrain the guttural sound of need that began somewhere deep in his chest and ended somewhere in Sherlock’s; his leg may have been weak but his arms were still good, still strong, and these he used to hold Sherlock against him, hearts pounding against each other.

Sherlock drew back and rubbed his lips exploratively over John’s bare cheek. “Shaved off my beard. Did you recognize me?”

A nod.

“When last did you eat, Sherlock? Where is Mycroft? I --”

John suddenly lost consciousness mid-sentence.

It happened so fast there was no time to prepare for it. He felt like a marionette whose strings had been cut, and just as before, John had no time to brace himself for the awful sensation of weightlessness until he splashed down hard.

He sank until his bare toes touched slimy, rotten wood. Columns of eerie lavender light threaded through the portholes of a magnificent old ship’s cabin; John looked around in astonishment. He was standing in the captain’s quarters of a sunken ship. Nature had run rampant here; sea vegetation grew over nearly every surface.

 _I can breathe water again_ , John thought, watching as an octopus climbed into a metal pot and changed its skin to match the rust spots there. _It’s a dream. I wonder if I should expect Undine._

The source of the unnatural pale purple light became apparent when John looked out of the porthole: jellyfish floated like ghosts in the foggy current. Their light illuminated the endless sea floor below, which was studded with sluggish brittle stars.

John wondered how many miles were between this ship and the surface of the sea. He investigated the rest of the cabin, captivated in particular by an oddly-shaped lump atop a small pillar. It was fluffily coated in some greyish scum. John scraped at it with his fingernail until a little stripe of marble was revealed.

It was a sculpture of a woman, with a square face and hooded, downturned eyes that made her smile seem sorrowful. She looked a little familiar. John ran his hand over the carefully-carved ringlets of her hair.

“ _Johnwatson._ ”

To his credit, John did not flinch.

He looked over his shoulder and saw Undine floating quietly in the hallway outside the cabin. He watched as she contorted her huge body carefully to fit through the human-sized door, pouring into the room until she filled it, and he turned to face her.

“ _You released mine own son from the web of promises in which he trapped himself._ ”

John nodded.

_“Interesting. I have given thought to your own request. I could return Sherlock’s Voice now.”_

John squared his shoulders. “I wasn’t born yesterday. What are your terms?”

Undine flashed a squaline smile.

“ _Say that you agree first._ ”

“No.”

“ _Do not misunderstand. You agree to mine own terms, or Sherlock stays voiceless forever._ ”

She loomed over him. The movement of her dark tail reminded John of an eel at market, writhing still seconds after its head had been chopped off. _Don’t do it, John Watson. If there is one thing in this world that you must not do, you must not accept this obviously skewed bargain --_

“Fine. I agree. What are your terms?” _Blast._

Undine slithered closer, her great body somehow not knocking over the piles of crates and furniture and luggage. As she moved, John thought he saw something a little strange on her body, but her arm moved and obscured it. “ _Don’t look so distraught, little meal. Nothing in this world is for free. You will owe me a good turn. That is all.”_

“Hah! What could I possibly do for you? I’m still not sure whether you are even real -- are you an apparition? I do not understand how it is I’ve come to be here,” replied John.

_“I chose to see you. It is a gift I withhold from mine own children. They would use it to fight each other even in their own dreams, and they war often enough in the woken times...”_

Undine put out her hand low near John’s feet. Her palm was as large as a hatbox lid. He belatedly understood that the mermaid wished for him to climb upon it; John did so, and she lifted him a few feet so they were face-to-face. Her eyes were the color of tiny organisms, primordial green things that had not yet learned the joys of land.

But -- there! Next to her wicked keel, John saw a deformed lump below the skin and above the heart. Jagged hemp rope was sewn cruelly through the infected skin.  _What the devil?_

Undine brought him close to her mouth and John contemplated leaping off of her hand.

“ _Aaaah. I will not eat you… today. Be still._ ”

She pursed her lips and blew, a single round bubble that encompassed John’s head with an undignified _blorp_ , and John inhaled sharply in startlement and inadvertently swallowed it, which had been her purpose all along. The Song ricocheted about in the echo chamber of the bubble. It sounded as a deep drone that rattled John’s bones, high-pitched operatic warbles, and what might have been distant laughter, all woven seamlessly together. Power flowed in through his ears and suffused his bones.

“Bloody hell,” whispered John, and his Voice came out complex. It sounded amazing, so he did it again. “I can feel it! Is… is it working?”

Undine smirked. “ _It is working."_

“I wonder…” John gazed at the metal pot on the floor. He hummed, wishing with all his might.

The octopus peeked out at him.

“Did I do that?” John asked.

“ _Doubtful,_ ” said Undine.

“Damn.”

“ _It takes time to learn how to Sing.”_

She lowered him to the floor. John cleared his throat. “Well. Thank you. It’s… a  bit startling to meet you, really. The way Mycroft told it, I thought Undine was just a myth.”

“ _So do most of mine own children. Too long I have been away from them. We are done for now. Go back to Sherlock... before you become unwilling to return what is not yours to keep.”_

John woke.

The first thing he saw, through the sheen of the bubble surrounding his head, was the abstract stretch of Sherlock’s face. Sherlock’s Voice crescendoed with excitement inside of the bubble, almost as though it recognized its original master.

 _What happened_? he mouthed, brow furrowed.

John cupped the back of Sherlock’s head, and drew him down. Sherlock resisted when his nose touched the edge of the bubble, shying away, but John just relaxed his grip and smiled patiently until the undine came to him of his own accord. Sherlock’s expression transformed when he heard the sound of his own Voice.

John leaned up to kiss him. The supernatural chorus funneled out of his mouth and back where it belonged, the bubble shrinking away. Sherlock started humming immediately, as though he could not wait for his voice to return completely.

The humming spoke to John, telling him that Sherlock would defend him with his life, even if the odds were overwhelming. Sherlock forgave him, and trusted he would be forgiven himself. Sherlock wanted to swim with him, to share their life experience in every conceivable way. The humming told him that when John eventually died, Sherlock would find some quiet abandoned beach and lie out until the sun took him, for a life without him would be a life half-lived.

“Mine own,” Sherlock purred. His rich baritone wove expertly through the chaotic sound of his own joyful Song. “You came back.”

John tried to sit up, but a gentle hand on his chest kept him flat on the rock. “You came back to me,” Sherlock repeated, drawing John back up and against his slender chest.

John gave up trying to move. He tilted his head back so he could look up into Sherlock’s face. “‘Course I came back.”

“Why?”

“I’m in love with you, you great fishy git. Against all sane counsel.”

Sherlock’s Song crescendoed briefly in pleasure. He had to raise his voice to be heard over it. “You kept Olizarat’s own tooth.”

“Yes.”

Sherlock ran the backs of his fingers softly down John’s neck, his chest -- so gentle it was as though he sensed the wound there -- and finally he smoothed his palms over John’s thighs. He did nothing impertinent despite the exciting proximity, but clever fingers did delve into John’s pocket.

“Oh.”

John licked his lips. “Mhm. Found it in the sand.”

Sherlock took the bullet out of John’s pocket and let it roll over the back of his knuckles, watching it gleam in the patch of moonlight that fell onto the stone bridge.

“This reminds me. There is one matter we must discuss, John… you still owe me a favor.”

John spluttered. “What?! I thought we were starting clean.”

Sherlock shook his head. “You chose to undo our negotiations. But I did not release you from your own agreement to me. As I recall: _One favor from me. Anything._ ” It was uncanny how Sherlock could mould his voice to become a different person when he wanted to, for it had been a perfect recitation of John’s voice, even down to the way John sometimes licked his own lip when he was thinking about what to say.

John tried to sit up again, but Sherlock’s arms tightened greedily.

“After all of this, what could you possibly want from me, Sherlock? I came back, didn’t I?”

“Marry me, John.”

“Sorry. What?”

Sherlock let John sit up this time, and the undine sank a little into the water as John shuffled around on the rock to get a good look at him.

The undine just looked steadily up at him. The moonlight shone on his porcelain skin and his inky tail occasionally shone in the deep as it swayed to keep him aloft. From this angle, one might not realize that Sherlock was not some heartrendingly beautiful boy. A beautiful boy that had just proposed to John like he was some blushing maiden.

“Erm,” said John.

“Mine own people understand better than anyone that caring is not an advantage. Look at how you wear around your neck Olizarat’s own tooth, that I gave you. Sentiment. I too am infected. See this.”

Sherlock flashed a glimpse of the bullet he was holding in one white-knuckled hand. “They will wear those rings for the rest of their lives, so everyone knows the depth of their regard, is that not what you said? You told me that if a man meets a woman and falls in love, he might propose to her. They agree to share everything, to be together until death do them part.”

Sherlock took John’s hands in his own, the bullet warm between John’s palms. His voice came out steady and confident, but there was the barest tremble in his touch that won John over immediately. “I want that. I want to share with you mine own life, the sea, mine own future Riptide, and mine own future lovers.”

John was ready to disagree, but then he remembered the feeling of Lestrade’s fingers when he had shaved John’s face, so strong and gentle. He thought about the power in undine bodies, wondered what it might feel like to have more than one surrounding him when he met his climax. And a part of him was curious to see what Sherlock looked like with a thick, curved undine member in his vent.

John shivered -- then he nodded firmly. _Oh, yes. I want that._

“Do not leave me, John. I promise you this --” the air crackled with power, “I will never force you to do anything that you do not wish to do again, and you may go wherever you wish, for always, anytime, as long as you come and see me when it suits you.”

John felt lightheaded.

  
“Your own life is so brief, mine own little love,” murmured Sherlock, stroking a short lock of hair away from John’s forehead. “But I will stay with you for all of it.”

**Notes for the Chapter:**

> Whelp. They'll never have a perfect relationship, but at least there's a little more communication happening.
> 
> I FINALLY GOT TO ACTIVATE A LOCATION I SET IN CHAPTER FUCKING 2, I AM SO HAPPY RIGHT NOW OH MY GOD I HAVE BEEN WAITING TO SHARE THIS MOMENT FOR A FREAKIN’ YEAR. ~fish confetti~ now I'm off to sleep, as usual you can check the update schedule on my blog, no need to ask here!

**Author's Note:**

> This story is a present for [Anarfea](http://archiveofourown.org/users/Anarfea/pseuds/Anarfea). Thanks to [JP](http://archiveofourown.org/users/JPerceval/pseuds/JPerceval), [Dee](http://archiveofourown.org/users/DraloreShimare), and [Redscudery](http://archiveofourown.org/users/redscudery/pseuds/redscudery) for beta reading! The Antidiogenes Club has my wriggliest gratitude for their joyful support of my exploration of Johnlock merman sexuality.
> 
> Comments _feed_ my plot piranhas, but pressure to update sooner _kills_ them!

**Works inspired by this one:**

  * [Riptide Lover fanart: 'In the Grotto'](https://archiveofourown.org/works/3221351) by [DulcimerGecko](https://archiveofourown.org/users/DulcimerGecko/pseuds/DulcimerGecko)
  * [Breathe for Me](https://archiveofourown.org/works/4079866) by [nosetothewind94](https://archiveofourown.org/users/nosetothewind94/pseuds/nosetothewind94)
  * [Cover Art for Riptide Lover](https://archiveofourown.org/works/4378073) by [yellowflashz](https://archiveofourown.org/users/yellowflashz/pseuds/yellowflashz)




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